HTML <!DOCTYPE>
HTML DOCTYPE Declaration
All HTML documents must start with a
<!DOCTYPE> declaration.
The doctype declaration is not an HTML tag. It is an "instruction" to the browser about what document type to expect.
The doctype declaration appears at the beginning of an HTML document, before
the <html> tag.
In HTML5, the <!DOCTYPE> declaration is simple:
<!DOCTYPE html>
Note: The <!DOCTYPE> declaration is not case-sensitive.
Other DOCTYPE Declarations
In older documents (HTML 4 or XHTML), the declaration is more complicated because the declaration must refer to a DTD (Document Type Definition).
HTML 4.01:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
XHTML 1.1:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
Valid HTML Elements in Different DOCTYPES
| Tag | HTML 5 | HTML 4 | XHTML |
|---|---|---|---|
| <a> | Yes | Yes | Yes |
| <abbr> | Yes | Yes | Yes |
| <acronym> | No | Yes | Yes |
| <address> | Yes | Yes | Yes |
| <applet> | No | Yes | No |
| <area> | Yes | Yes | No |
| <article> | Yes | No | No |
| <aside> | Yes | No | No |
| <audio> | Yes | No | No |
| <b> | Yes | Yes | Yes |
| <base> | Yes | Yes | Yes |
| <basefont> | No | Yes | No |
| <bdi> | Yes | No | No |
| <bdo> | Yes | Yes | No |
| <big> | No | Yes | Yes |
| <blockquote> | Yes | Yes | Yes |
| <body> | Yes | Yes | Yes |
| <br> | Yes | Yes | Yes |
| <button> | Yes | Yes | Yes |
| <canvas> | Yes | No | No |
| <caption> | Yes | Yes | Yes |
| <center> | No | Yes | No |
| <cite> | Yes | Yes | Yes |
| <code> | Yes | Yes | Yes |
| <col> | Yes | Yes | No |
| <colgroup> | Yes | Yes | No |
| <data> | Yes | No | No |
| <datalist> | Yes | No | No |
| <dd> | Yes | Yes | Yes |
| <del> | Yes | Yes | No |
| <details> | Yes | No | No |
| <dfn> | Yes | Yes | Yes |
| <dialog> | Yes | No | No |
| <dir> | No | Yes | No |
| <div> | Yes | Yes | Yes |
| <dl> | Yes | Yes | Yes |
| <dt> | Yes | Yes | Yes |
| <em> | Yes | Yes | Yes |
| <embed> | Yes | No | No |
| <fieldset> | Yes | Yes | Yes |
| <figcaption> | Yes | No | No |
| <figure> | Yes | No | No |
| <font> | No | Yes | No |
| <footer> | Yes | No | No |
| <form> | Yes | Yes | Yes |
| <frame> | No | Yes | No |
| <frameset> | No | Yes | No |
| <h1> to <h6> | Yes | Yes | Yes |
| <head> | Yes | Yes | Yes |
| <header> | Yes | No | No |
| <hr> | Yes | Yes | Yes |
| <html> | Yes | Yes | Yes |
| <i> | Yes | Yes | Yes |
| <iframe> | Yes | Yes | No |
| <img> | Yes | Yes | Yes |
| <input> | Yes | Yes | Yes |
| <ins> | Yes | Yes | No |
| <kbd> | Yes | Yes | Yes |
| <label> | Yes | Yes | Yes |
| <legend> | Yes | Yes | Yes |
| <li> | Yes | Yes | Yes |
| <link> | Yes | Yes | Yes |
| <main> | Yes | No | No |
| <map> | Yes | Yes | No |
| <mark> | Yes | No | No |
| <meta> | Yes | Yes | Yes |
| <meter> | Yes | No | No |
| <nav> | Yes | No | No |
| <noframes> | No | Yes | No |
| <noscript> | Yes | Yes | Yes |
| <object> | Yes | Yes | Yes |
| <ol> | Yes | Yes | Yes |
| <optgroup> | Yes | Yes | Yes |
| <option> | Yes | Yes | Yes |
| <output> | Yes | No | No |
| <p> | Yes | Yes | Yes |
| <param> | Yes | Yes | Yes |
| <picture> | Yes | No | No |
| <pre> | Yes | Yes | Yes |
| <progress> | Yes | No | No |
| <q> | Yes | Yes | Yes |
| <rp> | Yes | No | No |
| <rt> | Yes | No | No |
| <ruby> | Yes | No | No |
| <s> | Yes | Yes | No |
| <samp> | Yes | Yes | Yes |
| <script> | Yes | Yes | Yes |
| <section> | Yes | No | No |
| <select> | Yes | Yes | Yes |
| <small> | Yes | Yes | Yes |
| <source> | Yes | No | No |
| <span> | Yes | Yes | Yes |
| <strike> | No | Yes | No |
| <strong> | Yes | Yes | Yes |
| <style> | Yes | Yes | Yes |
| <sub> | Yes | Yes | Yes |
| <summary> | Yes | No | No |
| <sup> | Yes | Yes | Yes |
| <table> | Yes | Yes | Yes |
| <tbody> | Yes | Yes | No |
| <td> | Yes | Yes | Yes |
| <template> | Yes | No | No |
| <textarea> | Yes | Yes | Yes |
| <tfoot> | Yes | Yes | No |
| <th> | Yes | Yes | Yes |
| <thead> | Yes | Yes | No |
| <time> | Yes | No | No |
| <title> | Yes | Yes | Yes |
| <tr> | Yes | Yes | Yes |
| <track> | Yes | No | No |
| <tt> | No | Yes | Yes |
| <u> | Yes | Yes | No |
| <ul> | Yes | Yes | Yes |
| <var> | Yes | Yes | Yes |
| <video> | Yes | No | No |
| <wbr> | Yes | No | No |
