diff --git a/Cargo.toml b/Cargo.toml
index 1689cc2..6068a86 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "monolith"
-version = "2.0.19"
+version = "2.0.20"
 authors = [
     "Sunshine <sunshine@uberspace.net>",
     "Mahdi Robatipoor <mahdi.robatipoor@gmail.com>",
diff --git a/src/html.rs b/src/html.rs
index 33592fd..f13b542 100644
--- a/src/html.rs
+++ b/src/html.rs
@@ -5,62 +5,44 @@ use html5ever::serialize::{serialize, SerializeOpts};
 use html5ever::tendril::{format_tendril, TendrilSink};
 use html5ever::tree_builder::{Attribute, TreeSink};
 use html5ever::{local_name, namespace_url, ns};
-use http::{is_valid_url, resolve_url, retrieve_asset};
+use http::retrieve_asset;
+use js::attr_is_event_handler;
 use regex::Regex;
 use std::default::Default;
-use utils::data_to_dataurl;
+use utils::{data_to_dataurl, is_valid_url, resolve_url, url_has_protocol};
 
 lazy_static! {
     static ref EMPTY_STRING: String = String::new();
-    static ref HAS_PROTOCOL: Regex = Regex::new(r"^[a-z0-9]+:").unwrap();
-    static ref ICON_VALUES: Regex =
-        Regex::new(r"^icon|shortcut icon|mask-icon|apple-touch-icon|fluid-icon$").unwrap();
 }
 
+const ICON_VALUES: [&str; 5] = [
+    "icon",
+    "shortcut icon",
+    "mask-icon",
+    "apple-touch-icon",
+    "fluid-icon",
+];
+
 const TRANSPARENT_PIXEL: &str =
     "data:image/png;base64,\
      iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
 
-const JS_DOM_EVENT_ATTRS: [&str; 21] = [
-    // Input
-    "onfocus",
-    "onblur",
-    "onselect",
-    "onchange",
-    "onsubmit",
-    "onreset",
-    "onkeydown",
-    "onkeypress",
-    "onkeyup",
-    // Mouse
-    "onmouseover",
-    "onmouseout",
-    "onmousedown",
-    "onmouseup",
-    "onmousemove",
-    // Click
-    "onclick",
-    "ondblclick",
-    // Load
-    "onload",
-    "onunload",
-    "onabort",
-    "onerror",
-    "onresize",
-];
-
-fn get_parent_node(node: &Handle) -> Handle {
+pub fn get_parent_node(node: &Handle) -> Handle {
     let parent = node.parent.take().clone();
     parent.and_then(|node| node.upgrade()).unwrap()
 }
 
-fn get_node_name(node: &Handle) -> String {
+pub fn get_node_name(node: &Handle) -> String {
     match &node.data {
         NodeData::Element { ref name, .. } => name.local.as_ref().to_string(),
         _ => EMPTY_STRING.clone(),
     }
 }
 
+pub fn is_icon(attr_value: &str) -> bool {
+    ICON_VALUES.contains(&&*attr_value.to_lowercase())
+}
+
 pub fn walk_and_embed_assets(
     url: &str,
     node: &Handle,
@@ -239,7 +221,7 @@ pub fn walk_and_embed_assets(
                     for attr in attrs_mut.iter_mut() {
                         if &attr.name.local == "href" {
                             // Don't touch email links or hrefs which begin with a hash sign
-                            if attr.value.starts_with('#') || has_protocol(&attr.value) {
+                            if attr.value.starts_with('#') || url_has_protocol(&attr.value) {
                                 continue;
                             }
 
@@ -282,73 +264,68 @@ pub fn walk_and_embed_assets(
                 }
                 "style" => {
                     if opt_no_css {
-                        // Empty  inner content of STYLE tags
+                        // Empty inner content of STYLE tags
                         node.children.borrow_mut().clear();
                     }
                 }
                 "form" => {
                     for attr in attrs_mut.iter_mut() {
                         if &attr.name.local == "action" {
-                            // Don't modify action that's already a full URL
-                            if is_valid_url(&attr.value) {
-                                continue;
+                            // Modify action to be a full URL
+                            if !is_valid_url(&attr.value) {
+                                let href_full_url: String =
+                                    resolve_url(&url, &attr.value.to_string())
+                                        .unwrap_or(EMPTY_STRING.clone());
+                                attr.value.clear();
+                                attr.value.push_slice(href_full_url.as_str());
                             }
-
-                            let href_full_url: String = resolve_url(&url, &attr.value.to_string())
-                                .unwrap_or(EMPTY_STRING.clone());
-                            attr.value.clear();
-                            attr.value.push_slice(href_full_url.as_str());
                         }
                     }
                 }
                 "iframe" => {
-                    if opt_no_frames {
-                        // Empty the src attribute
-                        for attr in attrs_mut.iter_mut() {
-                            if &attr.name.local == "src" {
+                    for attr in attrs_mut.iter_mut() {
+                        if &attr.name.local == "src" {
+                            if opt_no_frames {
+                                // Empty the src attribute
                                 attr.value.clear();
+                                continue;
                             }
-                        }
-                    } else {
-                        for attr in attrs_mut.iter_mut() {
-                            if &attr.name.local == "src" {
-                                let iframe_src = attr.value.to_string();
 
-                                // Ignore iframes with empty source (they cause infinite loops)
-                                if iframe_src == EMPTY_STRING.clone() {
-                                    continue;
-                                }
+                            let iframe_src: String = attr.value.to_string();
 
-                                let src_full_url: String =
-                                    resolve_url(&url, &iframe_src).unwrap_or(EMPTY_STRING.clone());
-                                let iframe_data = retrieve_asset(
-                                    &src_full_url,
-                                    false,
-                                    "text/html",
-                                    opt_user_agent,
-                                    opt_silent,
-                                    opt_insecure,
-                                )
-                                .unwrap_or(EMPTY_STRING.clone());
-                                let dom = html_to_dom(&iframe_data);
-                                walk_and_embed_assets(
-                                    &src_full_url,
-                                    &dom.document,
-                                    opt_no_css,
-                                    opt_no_js,
-                                    opt_no_images,
-                                    opt_user_agent,
-                                    opt_silent,
-                                    opt_insecure,
-                                    opt_no_frames,
-                                );
-                                let mut buf: Vec<u8> = Vec::new();
-                                serialize(&mut buf, &dom.document, SerializeOpts::default())
-                                    .unwrap();
-                                let iframe_datauri = data_to_dataurl("text/html", &buf);
-                                attr.value.clear();
-                                attr.value.push_slice(iframe_datauri.as_str());
+                            // Ignore iframes with empty source (they cause infinite loops)
+                            if iframe_src == EMPTY_STRING.clone() {
+                                continue;
                             }
+
+                            let src_full_url: String =
+                                resolve_url(&url, &iframe_src).unwrap_or(EMPTY_STRING.clone());
+                            let iframe_data = retrieve_asset(
+                                &src_full_url,
+                                false,
+                                "text/html",
+                                opt_user_agent,
+                                opt_silent,
+                                opt_insecure,
+                            )
+                            .unwrap_or(EMPTY_STRING.clone());
+                            let dom = html_to_dom(&iframe_data);
+                            walk_and_embed_assets(
+                                &src_full_url,
+                                &dom.document,
+                                opt_no_css,
+                                opt_no_js,
+                                opt_no_images,
+                                opt_user_agent,
+                                opt_silent,
+                                opt_insecure,
+                                opt_no_frames,
+                            );
+                            let mut buf: Vec<u8> = Vec::new();
+                            serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+                            let iframe_datauri = data_to_dataurl("text/html", &buf);
+                            attr.value.clear();
+                            attr.value.push_slice(iframe_datauri.as_str());
                         }
                     }
                 }
@@ -357,7 +334,7 @@ pub fn walk_and_embed_assets(
                         if &attr.name.local == "poster" {
                             let video_poster = attr.value.to_string();
 
-                            // Ignore posters with empty source
+                            // Skip posters with empty source
                             if video_poster == EMPTY_STRING.clone() {
                                 continue;
                             }
@@ -387,20 +364,30 @@ pub fn walk_and_embed_assets(
 
             if opt_no_css {
                 // Get rid of style attributes
-                for attr in attrs_mut.iter_mut() {
+                let mut style_attr_indexes = Vec::new();
+                for (i, attr) in attrs_mut.iter_mut().enumerate() {
                     if attr.name.local.to_lowercase() == "style" {
-                        attr.value.clear();
+                        style_attr_indexes.push(i);
                     }
                 }
+                style_attr_indexes.reverse();
+                for attr_index in style_attr_indexes {
+                    attrs_mut.remove(attr_index);
+                }
             }
 
             if opt_no_js {
                 // Get rid of JS event attributes
-                for attr in attrs_mut.iter_mut() {
-                    if JS_DOM_EVENT_ATTRS.contains(&attr.name.local.to_lowercase().as_str()) {
-                        attr.value.clear();
+                let mut js_attr_indexes = Vec::new();
+                for (i, attr) in attrs_mut.iter_mut().enumerate() {
+                    if attr_is_event_handler(&attr.name.local) {
+                        js_attr_indexes.push(i);
                     }
                 }
+                js_attr_indexes.reverse();
+                for attr_index in js_attr_indexes {
+                    attrs_mut.remove(attr_index);
+                }
             }
 
             // Dig deeper
@@ -427,10 +414,6 @@ pub fn walk_and_embed_assets(
     }
 }
 
-fn has_protocol(url: &str) -> bool {
-    HAS_PROTOCOL.is_match(&url.to_lowercase())
-}
-
 pub fn html_to_dom(data: &str) -> html5ever::rcdom::RcDom {
     parse_document(RcDom::default(), Default::default())
         .from_utf8()
@@ -472,44 +455,45 @@ pub fn stringify_document(
         let doc = dom.get_document();
         let html = get_child_node_by_name(&doc, "html");
         let head = get_child_node_by_name(&html, "head");
-        {
-            let mut content_attr = EMPTY_STRING.clone();
-            if opt_isolate {
-                content_attr += "default-src 'unsafe-inline' data:;"
-            }
-            if opt_no_css {
-                content_attr += "style-src 'none';"
-            }
-            if opt_no_frames {
-                content_attr += "frame-src 'none';child-src 'none';"
-            }
-            if opt_no_js {
-                content_attr += "script-src 'none';"
-            }
-            if opt_no_images {
-                content_attr += "img-src data:;"
-            }
-            let meta = dom.create_element(
-                QualName::new(None, ns!(), local_name!("meta")),
-                vec![
-                    Attribute {
-                        name: QualName::new(None, ns!(), local_name!("http-equiv")),
-                        value: format_tendril!("Content-Security-Policy"),
-                    },
-                    Attribute {
-                        name: QualName::new(None, ns!(), local_name!("content")),
-                        value: format_tendril!("{}", content_attr),
-                    },
-                ],
-                Default::default(),
-            );
-            head.children.borrow_mut().reverse();
-            head.children.borrow_mut().push(meta.clone());
-            head.children.borrow_mut().reverse();
-            // Note: the CSP meta-tag has to be prepended, never appended,
-            //       since there already may be one defined in the document,
-            //       and browsers don't allow re-defining them (for obvious reasons)
+        let mut content_attr = EMPTY_STRING.clone();
+        if opt_isolate {
+            content_attr += " default-src 'unsafe-inline' data:;";
         }
+        if opt_no_css {
+            content_attr += " style-src 'none';";
+        }
+        if opt_no_frames {
+            content_attr += " frame-src 'none';child-src 'none';";
+        }
+        if opt_no_js {
+            content_attr += " script-src 'none';";
+        }
+        if opt_no_images {
+            content_attr += " img-src data:;";
+        }
+        content_attr = content_attr.trim().to_string();
+
+        let meta = dom.create_element(
+            QualName::new(None, ns!(), local_name!("meta")),
+            vec![
+                Attribute {
+                    name: QualName::new(None, ns!(), local_name!("http-equiv")),
+                    value: format_tendril!("Content-Security-Policy"),
+                },
+                Attribute {
+                    name: QualName::new(None, ns!(), local_name!("content")),
+                    value: format_tendril!("{}", content_attr),
+                },
+            ],
+            Default::default(),
+        );
+        head.children.borrow_mut().reverse();
+        head.children.borrow_mut().push(meta.clone());
+        head.children.borrow_mut().reverse();
+        // Note: the CSP meta-tag has to be prepended, never appended,
+        //       since there already may be one defined in the document,
+        //       and browsers don't allow re-defining them (for obvious reasons)
+
         serialize(&mut buf, &doc, SerializeOpts::default())
             .expect("unable to serialize DOM into buffer");
         result = String::from_utf8(buf).unwrap();
@@ -519,429 +503,3 @@ pub fn stringify_document(
 
     result
 }
-
-fn is_icon(attr_value: &str) -> bool {
-    ICON_VALUES.is_match(&attr_value.to_lowercase())
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_is_icon() {
-        assert_eq!(is_icon("icon"), true);
-        assert_eq!(is_icon("Shortcut Icon"), true);
-        assert_eq!(is_icon("ICON"), true);
-        assert_eq!(is_icon("mask-icon"), true);
-        assert_eq!(is_icon("fluid-icon"), true);
-        assert_eq!(is_icon("stylesheet"), false);
-        assert_eq!(is_icon(""), false);
-    }
-
-    #[test]
-    fn test_has_protocol() {
-        assert_eq!(
-            has_protocol("mailto:somebody@somewhere.com?subject=hello"),
-            true
-        );
-        assert_eq!(has_protocol("tel:5551234567"), true);
-        assert_eq!(has_protocol("ftp:user:password@some-ftp-server.com"), true);
-        assert_eq!(has_protocol("javascript:void(0)"), true);
-        assert_eq!(has_protocol("http://news.ycombinator.com"), true);
-        assert_eq!(has_protocol("https://github.com"), true);
-        assert_eq!(has_protocol("//some-hostname.com/some-file.html"), false);
-        assert_eq!(has_protocol("some-hostname.com/some-file.html"), false);
-        assert_eq!(has_protocol("/some-file.html"), false);
-        assert_eq!(has_protocol(""), false);
-        assert_eq!(
-            has_protocol("MAILTO:somebody@somewhere.com?subject=hello"),
-            true
-        );
-    }
-
-    #[test]
-    fn test_get_parent_node_name() {
-        let html = "<!doctype html><html><HEAD></HEAD><body><div><P></P></div></body></html>";
-        let dom = html_to_dom(&html);
-        let mut count = 0;
-
-        fn test_walk(node: &Handle, i: &mut i8) {
-            *i += 1;
-
-            match &node.data {
-                NodeData::Document => {
-                    for child in node.children.borrow().iter() {
-                        test_walk(child, &mut *i);
-                    }
-                }
-                NodeData::Doctype { .. } => (),
-                NodeData::Text { .. } => (),
-                NodeData::Comment { .. } => (),
-                NodeData::Element { ref name, .. } => {
-                    let node_name = name.local.as_ref().to_string();
-                    let parent_node_name = get_node_name(&get_parent_node(node));
-                    if node_name == "head" || node_name == "body" {
-                        assert_eq!(parent_node_name, "html");
-                    } else if node_name == "div" {
-                        assert_eq!(parent_node_name, "body");
-                    } else if node_name == "p" {
-                        assert_eq!(parent_node_name, "div");
-                    }
-
-                    println!("{}", node_name);
-
-                    for child in node.children.borrow().iter() {
-                        test_walk(child, &mut *i);
-                    }
-                }
-                NodeData::ProcessingInstruction { .. } => unreachable!(),
-            };
-        }
-
-        test_walk(&dom.document, &mut count);
-
-        assert_eq!(count, 7);
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets() {
-        let html = "<div><P></P></div>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head></head><body><div><p></p></div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets_no_recursive_iframe() {
-        let html = "<div><P></P><iframe src=\"\"></iframe></div>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head></head><body><div><p></p><iframe src=\"\"></iframe></div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets_no_css() {
-        let html = "<link rel=\"stylesheet\" href=\"main.css\">\
-                    <style>html{background-color: #000;}</style>\
-                    <div style=\"display: none;\"></div>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = true;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head><link rel=\"stylesheet\" href=\"\"><style></style></head>\
-             <body><div style=\"\"></div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets_no_images() {
-        let html = "<link rel=\"icon\" href=\"favicon.ico\">\
-                    <div><img src=\"http://localhost/assets/mono_lisa.png\" /></div>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = true;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head><link rel=\"icon\" href=\"\"></head><body><div>\
-             <img src=\"data:image/png;base64,\
-             iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0\
-             lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=\">\
-             </div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets_no_frames() {
-        let html = "<iframe src=\"http://trackbook.com\"></iframe>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = true;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head></head><body><iframe src=\"\"></iframe></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_walk_and_embed_assets_no_js() {
-        let html =
-            "<div onClick=\"void(0)\"><script src=\"http://localhost/assets/some.js\"></script>\
-             <script>alert(1)</script></div>";
-        let dom = html_to_dom(&html);
-        let url = "http://localhost";
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = true;
-        let opt_no_images: bool = false;
-        let opt_silent = true;
-        let opt_insecure = false;
-
-        walk_and_embed_assets(
-            &url,
-            &dom.document,
-            opt_no_css,
-            opt_no_js,
-            opt_no_images,
-            "",
-            opt_silent,
-            opt_insecure,
-            opt_no_frames,
-        );
-
-        let mut buf: Vec<u8> = Vec::new();
-        serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
-
-        assert_eq!(
-            buf.iter().map(|&c| c as char).collect::<String>(),
-            "<html><head></head><body><div onclick=\"\"><script src=\"\"></script>\
-             <script></script></div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_stringify_document() {
-        let html = "<div><script src=\"some.js\"></script></div>";
-        let dom = html_to_dom(&html);
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_isolate: bool = false;
-
-        assert_eq!(
-            stringify_document(
-                &dom.document,
-                opt_no_css,
-                opt_no_frames,
-                opt_no_js,
-                opt_no_images,
-                opt_isolate,
-            ),
-            "<html><head></head><body><div><script src=\"some.js\"></script></div></body></html>"
-        );
-    }
-
-    #[test]
-    fn test_stringify_document_isolate() {
-        let html = "<title>Isolated document</title><link rel=\"something\"/>\
-                    <div><script src=\"some.js\"></script></div>";
-        let dom = html_to_dom(&html);
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_isolate: bool = true;
-
-        assert_eq!(
-            stringify_document(
-                &dom.document,
-                opt_no_css,
-                opt_no_frames,
-                opt_no_js,
-                opt_no_images,
-                opt_isolate,
-            ),
-            "<html>\
-             <head>\
-             <meta \
-             http-equiv=\"Content-Security-Policy\" \
-             content=\"default-src 'unsafe-inline' data:;\"></meta>\
-             <title>Isolated document</title>\
-             <link rel=\"something\">\
-             </head>\
-             <body><div><script src=\"some.js\"></script></div></body>\
-             </html>"
-        );
-    }
-
-    #[test]
-    fn test_stringify_document_no_css() {
-        let html = "<!doctype html>\
-                    <title>Unstyled document</title>\
-                    <link rel=\"stylesheet\" href=\"main.css\"/>\
-                    <div style=\"display: none;\"></div>";
-        let dom = html_to_dom(&html);
-
-        let opt_no_css: bool = true;
-        let opt_no_frames: bool = false;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_isolate: bool = false;
-
-        assert_eq!(
-            stringify_document(
-                &dom.document,
-                opt_no_css,
-                opt_no_frames,
-                opt_no_js,
-                opt_no_images,
-                opt_isolate,
-            ),
-            "<!DOCTYPE html>\
-             <html>\
-             <head>\
-             <meta http-equiv=\"Content-Security-Policy\" content=\"style-src 'none';\"></meta>\
-             <title>Unstyled document</title>\
-             <link rel=\"stylesheet\" href=\"main.css\">\
-             </head>\
-             <body><div style=\"display: none;\"></div></body>\
-             </html>"
-        );
-    }
-
-    #[test]
-    fn test_stringify_document_no_frames() {
-        let html = "<!doctype html><title>Frameless document</title><link rel=\"something\"/>\
-                    <div><script src=\"some.js\"></script></div>";
-        let dom = html_to_dom(&html);
-
-        let opt_no_css: bool = false;
-        let opt_no_frames: bool = true;
-        let opt_no_js: bool = false;
-        let opt_no_images: bool = false;
-        let opt_isolate: bool = false;
-
-        assert_eq!(
-            stringify_document(
-                &dom.document,
-                opt_no_css,
-                opt_no_frames,
-                opt_no_js,
-                opt_no_images,
-                opt_isolate,
-            ),
-            "<!DOCTYPE html>\
-             <html>\
-             <head>\
-             <meta http-equiv=\"Content-Security-Policy\" content=\"frame-src 'none';child-src 'none';\"></meta>\
-             <title>Frameless document</title>\
-             <link rel=\"something\">\
-             </head>\
-             <body><div><script src=\"some.js\"></script></div></body>\
-             </html>"
-        );
-    }
-}
diff --git a/src/http.rs b/src/http.rs
index 50d686b..fe5e3ae 100644
--- a/src/http.rs
+++ b/src/http.rs
@@ -1,35 +1,7 @@
-use regex::Regex;
 use reqwest::header::{CONTENT_TYPE, USER_AGENT};
 use reqwest::Client;
 use std::time::Duration;
-use url::{ParseError, Url};
-use utils::data_to_dataurl;
-
-lazy_static! {
-    static ref REGEX_URL: Regex = Regex::new(r"^https?://").unwrap();
-}
-
-pub fn is_data_url(url: &str) -> Result<bool, ParseError> {
-    match Url::parse(url) {
-        Ok(parsed_url) => Ok(parsed_url.scheme() == "data"),
-        Err(err) => Err(err),
-    }
-}
-
-pub fn is_valid_url(path: &str) -> bool {
-    REGEX_URL.is_match(path)
-}
-
-pub fn resolve_url(from: &str, to: &str) -> Result<String, ParseError> {
-    let result = if is_valid_url(to) {
-        // (anything, http://site.com/css/main.css)
-        to.to_string()
-    } else {
-        Url::parse(from)?.join(to)?.to_string()
-    };
-
-    Ok(result)
-}
+use utils::{data_to_dataurl, is_data_url};
 
 pub fn retrieve_asset(
     url: &str,
@@ -79,93 +51,3 @@ pub fn retrieve_asset(
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_is_valid_url() {
-        assert!(is_valid_url("https://www.rust-lang.org/"));
-        assert!(is_valid_url("http://kernel.org"));
-        assert!(!is_valid_url("//kernel.org"));
-        assert!(!is_valid_url("./index.html"));
-        assert!(!is_valid_url("some-local-page.htm"));
-        assert!(!is_valid_url("ftp://1.2.3.4/www/index.html"));
-        assert!(!is_valid_url(
-            "data:text/html;base64,V2VsY29tZSBUbyBUaGUgUGFydHksIDxiPlBhbDwvYj4h"
-        ));
-    }
-
-    #[test]
-    fn test_resolve_url() -> Result<(), ParseError> {
-        let resolved_url = resolve_url("https://www.kernel.org", "../category/signatures.html")?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.kernel.org/category/signatures.html"
-        );
-
-        let resolved_url = resolve_url("https://www.kernel.org", "category/signatures.html")?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.kernel.org/category/signatures.html"
-        );
-
-        let resolved_url = resolve_url(
-            "saved_page.htm",
-            "https://www.kernel.org/category/signatures.html",
-        )?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.kernel.org/category/signatures.html"
-        );
-
-        let resolved_url = resolve_url(
-            "https://www.kernel.org",
-            "//www.kernel.org/theme/images/logos/tux.png",
-        )?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.kernel.org/theme/images/logos/tux.png"
-        );
-
-        let resolved_url = resolve_url(
-            "https://www.kernel.org",
-            "//another-host.org/theme/images/logos/tux.png",
-        )?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://another-host.org/theme/images/logos/tux.png"
-        );
-
-        let resolved_url = resolve_url(
-            "https://www.kernel.org/category/signatures.html",
-            "/theme/images/logos/tux.png",
-        )?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.kernel.org/theme/images/logos/tux.png"
-        );
-
-        let resolved_url = resolve_url(
-            "https://www.w3schools.com/html/html_iframe.asp",
-            "default.asp",
-        )?;
-        assert_eq!(
-            resolved_url.as_str(),
-            "https://www.w3schools.com/html/default.asp"
-        );
-
-        Ok(())
-    }
-
-    #[test]
-    fn test_is_data_url() {
-        assert!(
-            is_data_url("data:text/html;base64,V2VsY29tZSBUbyBUaGUgUGFydHksIDxiPlBhbDwvYj4h")
-                .unwrap_or(false)
-        );
-        assert!(!is_data_url("https://kernel.org").unwrap_or(false));
-        assert!(!is_data_url("//kernel.org").unwrap_or(false));
-    }
-}
diff --git a/src/js.rs b/src/js.rs
new file mode 100644
index 0000000..32f946c
--- /dev/null
+++ b/src/js.rs
@@ -0,0 +1,32 @@
+const JS_DOM_EVENT_ATTRS: [&str; 21] = [
+    // Input
+    "onfocus",
+    "onblur",
+    "onselect",
+    "onchange",
+    "onsubmit",
+    "onreset",
+    "onkeydown",
+    "onkeypress",
+    "onkeyup",
+    // Mouse
+    "onmouseover",
+    "onmouseout",
+    "onmousedown",
+    "onmouseup",
+    "onmousemove",
+    // Click
+    "onclick",
+    "ondblclick",
+    // Load
+    "onload",
+    "onunload",
+    "onabort",
+    "onerror",
+    "onresize",
+];
+
+// Returns true if DOM attribute name matches a native JavaScript event handler
+pub fn attr_is_event_handler(attr_name: &str) -> bool {
+    JS_DOM_EVENT_ATTRS.contains(&attr_name.to_lowercase().as_str())
+}
diff --git a/src/lib.rs b/src/lib.rs
index 5ac119b..89f168c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,4 +7,8 @@ extern crate url;
 
 pub mod html;
 pub mod http;
+pub mod js;
 pub mod utils;
+
+#[cfg(test)]
+pub mod tests;
diff --git a/src/main.rs b/src/main.rs
index 2c88e22..ff1d29c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,9 +4,10 @@ extern crate monolith;
 
 use clap::{App, Arg};
 use monolith::html::{html_to_dom, stringify_document, walk_and_embed_assets};
-use monolith::http::{is_valid_url, retrieve_asset};
+use monolith::http::retrieve_asset;
+use monolith::utils::is_valid_url;
 
-static DEFAULT_USER_AGENT: &str =
+const DEFAULT_USER_AGENT: &str =
     "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:66.0) Gecko/20100101 Firefox/66.0";
 
 fn main() {
diff --git a/src/tests/html.rs b/src/tests/html.rs
new file mode 100644
index 0000000..11de822
--- /dev/null
+++ b/src/tests/html.rs
@@ -0,0 +1,467 @@
+use crate::html::{
+    get_node_name, get_parent_node, html_to_dom, is_icon, stringify_document, walk_and_embed_assets,
+};
+use html5ever::rcdom::{Handle, NodeData};
+use html5ever::serialize::{serialize, SerializeOpts};
+
+#[test]
+fn test_is_icon() {
+    assert_eq!(is_icon("icon"), true);
+    assert_eq!(is_icon("Shortcut Icon"), true);
+    assert_eq!(is_icon("ICON"), true);
+    assert_eq!(is_icon("mask-icon"), true);
+    assert_eq!(is_icon("fluid-icon"), true);
+    assert_eq!(is_icon("stylesheet"), false);
+    assert_eq!(is_icon(""), false);
+}
+
+#[test]
+fn test_get_parent_node_name() {
+    let html = "<!doctype html><html><HEAD></HEAD><body><div><P></P></div></body></html>";
+    let dom = html_to_dom(&html);
+    let mut count = 0;
+
+    fn test_walk(node: &Handle, i: &mut i8) {
+        *i += 1;
+
+        match &node.data {
+            NodeData::Document => {
+                for child in node.children.borrow().iter() {
+                    test_walk(child, &mut *i);
+                }
+            }
+            NodeData::Element { ref name, .. } => {
+                let node_name = name.local.as_ref().to_string();
+                let parent_node_name = get_node_name(&get_parent_node(node));
+                if node_name == "head" || node_name == "body" {
+                    assert_eq!(parent_node_name, "html");
+                } else if node_name == "div" {
+                    assert_eq!(parent_node_name, "body");
+                } else if node_name == "p" {
+                    assert_eq!(parent_node_name, "div");
+                }
+
+                println!("{}", node_name);
+
+                for child in node.children.borrow().iter() {
+                    test_walk(child, &mut *i);
+                }
+            }
+            _ => (),
+        };
+    }
+
+    test_walk(&dom.document, &mut count);
+
+    assert_eq!(count, 7);
+}
+
+#[test]
+fn test_walk_and_embed_assets() {
+    let html = "<div><P></P></div>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html><head></head><body><div><p></p></div></body></html>"
+    );
+}
+
+#[test]
+fn test_walk_and_embed_assets_ensure_no_recursive_iframe() {
+    let html = "<div><P></P><iframe src=\"\"></iframe></div>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html><head></head><body><div><p></p><iframe src=\"\"></iframe></div></body></html>"
+    );
+}
+
+#[test]
+fn test_walk_and_embed_assets_no_css() {
+    let html = "<link rel=\"stylesheet\" href=\"main.css\">\
+                <style>html{background-color: #000;}</style>\
+                <div style=\"display: none;\"></div>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = true;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html>\
+         <head>\
+         <link rel=\"stylesheet\" href=\"\">\
+         <style></style>\
+         </head>\
+         <body>\
+         <div></div>\
+         </body>\
+         </html>"
+    );
+}
+
+#[test]
+fn test_walk_and_embed_assets_no_images() {
+    let html = "<link rel=\"icon\" href=\"favicon.ico\">\
+                <div><img src=\"http://localhost/assets/mono_lisa.png\" /></div>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = true;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html>\
+         <head>\
+         <link rel=\"icon\" href=\"\">\
+         </head>\
+         <body>\
+         <div>\
+         <img src=\"data:image/png;base64,\
+         iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0\
+         lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=\">\
+         </div>\
+         </body>\
+         </html>"
+    );
+}
+
+#[test]
+fn test_walk_and_embed_assets_no_frames() {
+    let html = "<iframe src=\"http://trackbook.com\"></iframe>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = true;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html><head></head><body><iframe src=\"\"></iframe></body></html>"
+    );
+}
+
+#[test]
+fn test_walk_and_embed_assets_no_js() {
+    let html = "<div onClick=\"void(0)\">\
+                <script src=\"http://localhost/assets/some.js\"></script>\
+                <script>alert(1)</script>\
+                </div>";
+    let dom = html_to_dom(&html);
+    let url = "http://localhost";
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = true;
+    let opt_no_images: bool = false;
+    let opt_silent = true;
+    let opt_insecure = false;
+
+    walk_and_embed_assets(
+        &url,
+        &dom.document,
+        opt_no_css,
+        opt_no_js,
+        opt_no_images,
+        "",
+        opt_silent,
+        opt_insecure,
+        opt_no_frames,
+    );
+
+    let mut buf: Vec<u8> = Vec::new();
+    serialize(&mut buf, &dom.document, SerializeOpts::default()).unwrap();
+
+    assert_eq!(
+        buf.iter().map(|&c| c as char).collect::<String>(),
+        "<html><head></head><body><div><script src=\"\"></script>\
+         <script></script></div></body></html>"
+    );
+}
+
+#[test]
+fn test_stringify_document() {
+    let html = "<div><script src=\"some.js\"></script></div>";
+    let dom = html_to_dom(&html);
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_isolate: bool = false;
+
+    assert_eq!(
+        stringify_document(
+            &dom.document,
+            opt_no_css,
+            opt_no_frames,
+            opt_no_js,
+            opt_no_images,
+            opt_isolate,
+        ),
+        "<html><head></head><body><div><script src=\"some.js\"></script></div></body></html>"
+    );
+}
+
+#[test]
+fn test_stringify_document_isolate() {
+    let html = "<title>Isolated document</title>\
+                <link rel=\"something\" href=\"some.css\" />\
+                <meta http-equiv=\"Content-Security-Policy\" content=\"default-src https:\">\
+                <div><script src=\"some.js\"></script></div>";
+    let dom = html_to_dom(&html);
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_isolate: bool = true;
+
+    assert_eq!(
+        stringify_document(
+            &dom.document,
+            opt_no_css,
+            opt_no_frames,
+            opt_no_js,
+            opt_no_images,
+            opt_isolate,
+        ),
+        "<html>\
+            <head>\
+                <meta http-equiv=\"Content-Security-Policy\" content=\"default-src 'unsafe-inline' data:;\"></meta>\
+                <title>Isolated document</title>\
+                <link rel=\"something\" href=\"some.css\">\
+                <meta http-equiv=\"Content-Security-Policy\" content=\"default-src https:\">\
+            </head>\
+            <body>\
+                <div>\
+                    <script src=\"some.js\"></script>\
+                </div>\
+            </body>\
+         </html>"
+    );
+}
+
+#[test]
+fn test_stringify_document_no_css() {
+    let html = "<!doctype html>\
+                <title>Unstyled document</title>\
+                <link rel=\"stylesheet\" href=\"main.css\"/>\
+                <div style=\"display: none;\"></div>";
+    let dom = html_to_dom(&html);
+
+    let opt_no_css: bool = true;
+    let opt_no_frames: bool = false;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_isolate: bool = false;
+
+    assert_eq!(
+        stringify_document(
+            &dom.document,
+            opt_no_css,
+            opt_no_frames,
+            opt_no_js,
+            opt_no_images,
+            opt_isolate,
+        ),
+        "<!DOCTYPE html>\
+         <html>\
+         <head>\
+         <meta http-equiv=\"Content-Security-Policy\" content=\"style-src 'none';\"></meta>\
+         <title>Unstyled document</title>\
+         <link rel=\"stylesheet\" href=\"main.css\">\
+         </head>\
+         <body><div style=\"display: none;\"></div></body>\
+         </html>"
+    );
+}
+
+#[test]
+fn test_stringify_document_no_frames() {
+    let html = "<!doctype html>\
+                <title>Frameless document</title>\
+                <link rel=\"something\"/>\
+                <div><script src=\"some.js\"></script></div>";
+    let dom = html_to_dom(&html);
+
+    let opt_no_css: bool = false;
+    let opt_no_frames: bool = true;
+    let opt_no_js: bool = false;
+    let opt_no_images: bool = false;
+    let opt_isolate: bool = false;
+
+    assert_eq!(
+        stringify_document(
+            &dom.document,
+            opt_no_css,
+            opt_no_frames,
+            opt_no_js,
+            opt_no_images,
+            opt_isolate,
+        ),
+        "<!DOCTYPE html>\
+            <html>\
+            <head>\
+            <meta http-equiv=\"Content-Security-Policy\" content=\"frame-src 'none';child-src 'none';\"></meta>\
+            <title>Frameless document</title>\
+            <link rel=\"something\">\
+            </head>\
+            <body><div><script src=\"some.js\"></script></div></body>\
+            </html>"
+    );
+}
+
+#[test]
+fn test_stringify_document_isolate_no_frames_no_js_no_css_no_images() {
+    let html = "<!doctype html>\
+                <title>no-frame no-css no-js no-image isolated document</title>\
+                <meta http-equiv=\"Content-Security-Policy\" content=\"default-src https:\">\
+                <link rel=\"stylesheet\" href=\"some.css\">\
+                <div>\
+                <script src=\"some.js\"></script>\
+                <img style=\"width: 100%;\" src=\"some.png\" />\
+                <iframe src=\"some.html\"></iframe>\
+                </div>";
+    let dom = html_to_dom(&html);
+
+    let opt_isolate: bool = true;
+    let opt_no_css: bool = true;
+    let opt_no_frames: bool = true;
+    let opt_no_js: bool = true;
+    let opt_no_images: bool = true;
+
+    assert_eq!(
+        stringify_document(
+            &dom.document,
+            opt_no_css,
+            opt_no_frames,
+            opt_no_js,
+            opt_no_images,
+            opt_isolate,
+        ),
+        "<!DOCTYPE html>\
+            <html>\
+                <head>\
+                    <meta http-equiv=\"Content-Security-Policy\" content=\"default-src \'unsafe-inline\' data:; style-src \'none\'; frame-src \'none\';child-src \'none\'; script-src \'none\'; img-src data:;\"></meta>\
+                    <title>no-frame no-css no-js no-image isolated document</title>\
+                    <meta http-equiv=\"Content-Security-Policy\" content=\"default-src https:\">\
+                    <link rel=\"stylesheet\" href=\"some.css\">\
+                </head>\
+                <body>\
+                    <div>\
+                        <script src=\"some.js\"></script>\
+                        <img style=\"width: 100%;\" src=\"some.png\">\
+                        <iframe src=\"some.html\"></iframe>\
+                    </div>\
+                </body>\
+            </html>"
+    );
+}
diff --git a/src/tests/js.rs b/src/tests/js.rs
new file mode 100644
index 0000000..30ebda8
--- /dev/null
+++ b/src/tests/js.rs
@@ -0,0 +1,13 @@
+use crate::js::attr_is_event_handler;
+
+#[test]
+fn test_attr_is_event_handler() {
+    // succeeding
+    assert!(attr_is_event_handler("onBlur"));
+    assert!(attr_is_event_handler("onclick"));
+    assert!(attr_is_event_handler("onClick"));
+    // failing
+    assert!(!attr_is_event_handler("href"));
+    assert!(!attr_is_event_handler(""));
+    assert!(!attr_is_event_handler("class"));
+}
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
new file mode 100644
index 0000000..2efe36b
--- /dev/null
+++ b/src/tests/mod.rs
@@ -0,0 +1,3 @@
+mod html;
+mod js;
+mod utils;
diff --git a/src/tests/utils.rs b/src/tests/utils.rs
new file mode 100644
index 0000000..facfd9f
--- /dev/null
+++ b/src/tests/utils.rs
@@ -0,0 +1,160 @@
+use crate::utils::{
+    data_to_dataurl, detect_mimetype, is_data_url, is_valid_url, resolve_url, url_has_protocol,
+};
+use url::ParseError;
+
+#[test]
+fn test_data_to_dataurl() {
+    let mime = "application/javascript";
+    let data = "var word = 'hello';\nalert(word);\n";
+    let datauri = data_to_dataurl(mime, data.as_bytes());
+    assert_eq!(
+        &datauri,
+        "data:application/javascript;base64,dmFyIHdvcmQgPSAnaGVsbG8nOwphbGVydCh3b3JkKTsK"
+    );
+}
+
+#[test]
+fn test_detect_mimetype() {
+    // image
+    assert_eq!(detect_mimetype(b"GIF87a"), "image/gif");
+    assert_eq!(detect_mimetype(b"GIF89a"), "image/gif");
+    assert_eq!(detect_mimetype(b"\xFF\xD8\xFF"), "image/jpeg");
+    assert_eq!(detect_mimetype(b"\x89PNG\x0D\x0A\x1A\x0A"), "image/png");
+    assert_eq!(detect_mimetype(b"<?xml "), "image/svg+xml");
+    assert_eq!(detect_mimetype(b"<svg "), "image/svg+xml");
+    assert_eq!(detect_mimetype(b"RIFF....WEBPVP8 "), "image/webp");
+    assert_eq!(detect_mimetype(b"\x00\x00\x01\x00"), "image/x-icon");
+    // audio
+    assert_eq!(detect_mimetype(b"ID3"), "audio/mpeg");
+    assert_eq!(detect_mimetype(b"\xFF\x0E"), "audio/mpeg");
+    assert_eq!(detect_mimetype(b"\xFF\x0F"), "audio/mpeg");
+    assert_eq!(detect_mimetype(b"OggS"), "audio/ogg");
+    assert_eq!(detect_mimetype(b"RIFF....WAVEfmt "), "audio/wav");
+    assert_eq!(detect_mimetype(b"fLaC"), "audio/x-flac");
+    // video
+    assert_eq!(detect_mimetype(b"RIFF....AVI LIST"), "video/avi");
+    assert_eq!(detect_mimetype(b"....ftyp"), "video/mp4");
+    assert_eq!(detect_mimetype(b"\x00\x00\x01\x0B"), "video/mpeg");
+    assert_eq!(detect_mimetype(b"....moov"), "video/quicktime");
+    assert_eq!(detect_mimetype(b"\x1A\x45\xDF\xA3"), "video/webm");
+}
+
+#[test]
+fn test_url_has_protocol() {
+    // succeeding
+    assert_eq!(
+        url_has_protocol("mailto:somebody@somewhere.com?subject=hello"),
+        true
+    );
+    assert_eq!(url_has_protocol("tel:5551234567"), true);
+    assert_eq!(
+        url_has_protocol("ftp:user:password@some-ftp-server.com"),
+        true
+    );
+    assert_eq!(url_has_protocol("javascript:void(0)"), true);
+    assert_eq!(url_has_protocol("http://news.ycombinator.com"), true);
+    assert_eq!(url_has_protocol("https://github.com"), true);
+    assert_eq!(
+        url_has_protocol("MAILTO:somebody@somewhere.com?subject=hello"),
+        true
+    );
+    // failing
+    assert_eq!(
+        url_has_protocol("//some-hostname.com/some-file.html"),
+        false
+    );
+    assert_eq!(url_has_protocol("some-hostname.com/some-file.html"), false);
+    assert_eq!(url_has_protocol("/some-file.html"), false);
+    assert_eq!(url_has_protocol(""), false);
+}
+
+#[test]
+fn test_is_valid_url() {
+    // succeeding
+    assert!(is_valid_url("https://www.rust-lang.org/"));
+    assert!(is_valid_url("http://kernel.org"));
+    // failing
+    assert!(!is_valid_url("//kernel.org"));
+    assert!(!is_valid_url("./index.html"));
+    assert!(!is_valid_url("some-local-page.htm"));
+    assert!(!is_valid_url("ftp://1.2.3.4/www/index.html"));
+    assert!(!is_valid_url(
+        "data:text/html;base64,V2VsY29tZSBUbyBUaGUgUGFydHksIDxiPlBhbDwvYj4h"
+    ));
+}
+
+#[test]
+fn test_resolve_url() -> Result<(), ParseError> {
+    let resolved_url = resolve_url("https://www.kernel.org", "../category/signatures.html")?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.kernel.org/category/signatures.html"
+    );
+
+    let resolved_url = resolve_url("https://www.kernel.org", "category/signatures.html")?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.kernel.org/category/signatures.html"
+    );
+
+    let resolved_url = resolve_url(
+        "saved_page.htm",
+        "https://www.kernel.org/category/signatures.html",
+    )?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.kernel.org/category/signatures.html"
+    );
+
+    let resolved_url = resolve_url(
+        "https://www.kernel.org",
+        "//www.kernel.org/theme/images/logos/tux.png",
+    )?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.kernel.org/theme/images/logos/tux.png"
+    );
+
+    let resolved_url = resolve_url(
+        "https://www.kernel.org",
+        "//another-host.org/theme/images/logos/tux.png",
+    )?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://another-host.org/theme/images/logos/tux.png"
+    );
+
+    let resolved_url = resolve_url(
+        "https://www.kernel.org/category/signatures.html",
+        "/theme/images/logos/tux.png",
+    )?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.kernel.org/theme/images/logos/tux.png"
+    );
+
+    let resolved_url = resolve_url(
+        "https://www.w3schools.com/html/html_iframe.asp",
+        "default.asp",
+    )?;
+    assert_eq!(
+        resolved_url.as_str(),
+        "https://www.w3schools.com/html/default.asp"
+    );
+
+    Ok(())
+}
+
+#[test]
+fn test_is_data_url() {
+    // succeeding
+    assert!(
+        is_data_url("data:text/html;base64,V2VsY29tZSBUbyBUaGUgUGFydHksIDxiPlBhbDwvYj4h")
+            .unwrap_or(false)
+    );
+    // failing
+    assert!(!is_data_url("https://kernel.org").unwrap_or(false));
+    assert!(!is_data_url("//kernel.org").unwrap_or(false));
+    assert!(!is_data_url("").unwrap_or(false));
+}
diff --git a/src/utils.rs b/src/utils.rs
index 8f1e653..61a5d83 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -1,6 +1,13 @@
 extern crate base64;
 
 use self::base64::encode;
+use regex::Regex;
+use url::{ParseError, Url};
+
+lazy_static! {
+    static ref HAS_PROTOCOL: Regex = Regex::new(r"^[a-z0-9]+:").unwrap();
+    static ref REGEX_URL: Regex = Regex::new(r"^https?://").unwrap();
+}
 
 static MAGIC: [[&[u8]; 2]; 19] = [
     // Image
@@ -36,7 +43,7 @@ pub fn data_to_dataurl(mime: &str, data: &[u8]) -> String {
     format!("data:{};base64,{}", mimetype, encode(data))
 }
 
-fn detect_mimetype(data: &[u8]) -> String {
+pub fn detect_mimetype(data: &[u8]) -> String {
     let mut re = String::new();
 
     for item in MAGIC.iter() {
@@ -49,44 +56,27 @@ fn detect_mimetype(data: &[u8]) -> String {
     re
 }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
+pub fn url_has_protocol(url: &str) -> bool {
+    HAS_PROTOCOL.is_match(&url.to_lowercase())
+}
 
-    #[test]
-    fn test_data_to_dataurl() {
-        let mime = "application/javascript";
-        let data = "var word = 'hello';\nalert(word);\n";
-        let datauri = data_to_dataurl(mime, data.as_bytes());
-        assert_eq!(
-            &datauri,
-            "data:application/javascript;base64,dmFyIHdvcmQgPSAnaGVsbG8nOwphbGVydCh3b3JkKTsK"
-        );
-    }
-
-    #[test]
-    fn test_detect_mimetype() {
-        // Image
-        assert_eq!(detect_mimetype(b"GIF87a"), "image/gif");
-        assert_eq!(detect_mimetype(b"GIF89a"), "image/gif");
-        assert_eq!(detect_mimetype(b"\xFF\xD8\xFF"), "image/jpeg");
-        assert_eq!(detect_mimetype(b"\x89PNG\x0D\x0A\x1A\x0A"), "image/png");
-        assert_eq!(detect_mimetype(b"<?xml "), "image/svg+xml");
-        assert_eq!(detect_mimetype(b"<svg "), "image/svg+xml");
-        assert_eq!(detect_mimetype(b"RIFF....WEBPVP8 "), "image/webp");
-        assert_eq!(detect_mimetype(b"\x00\x00\x01\x00"), "image/x-icon");
-        // Audio
-        assert_eq!(detect_mimetype(b"ID3"), "audio/mpeg");
-        assert_eq!(detect_mimetype(b"\xFF\x0E"), "audio/mpeg");
-        assert_eq!(detect_mimetype(b"\xFF\x0F"), "audio/mpeg");
-        assert_eq!(detect_mimetype(b"OggS"), "audio/ogg");
-        assert_eq!(detect_mimetype(b"RIFF....WAVEfmt "), "audio/wav");
-        assert_eq!(detect_mimetype(b"fLaC"), "audio/x-flac");
-        // Video
-        assert_eq!(detect_mimetype(b"RIFF....AVI LIST"), "video/avi");
-        assert_eq!(detect_mimetype(b"....ftyp"), "video/mp4");
-        assert_eq!(detect_mimetype(b"\x00\x00\x01\x0B"), "video/mpeg");
-        assert_eq!(detect_mimetype(b"....moov"), "video/quicktime");
-        assert_eq!(detect_mimetype(b"\x1A\x45\xDF\xA3"), "video/webm");
+pub fn is_data_url(url: &str) -> Result<bool, ParseError> {
+    match Url::parse(url) {
+        Ok(parsed_url) => Ok(parsed_url.scheme() == "data"),
+        Err(err) => Err(err),
     }
 }
+
+pub fn is_valid_url(path: &str) -> bool {
+    REGEX_URL.is_match(path)
+}
+
+pub fn resolve_url(from: &str, to: &str) -> Result<String, ParseError> {
+    let result = if is_valid_url(to) {
+        to.to_string()
+    } else {
+        Url::parse(from)?.join(to)?.to_string()
+    };
+
+    Ok(result)
+}