The table below summarizes Web standards supported by WebHACC. See following subsections for more details.
| Standard | Version | Note | 
|---|---|---|
| HTML | HTML5 Draft Recommendation | Most parts | 
| XHTML | ||
| Atom | Atom 1.0 RFC | |
| Atom Threading 1.0 RFC | ||
| XML | 1.0 Fourth Edition | Tentative | 
| 1.1 Second Edition | Tentative | |
| XML Namespaces | 1.0 Second Edition | Tentative | 
| 1.1 First Edition | Tentative | |
| CSS | CSS 2.1 Candidate Recommendation | Most parts | 
| CSS Color Level 3 LCWD | Most parts | |
| Selectors | 3 | |
| Cache Manifest | HTML5 Draft Recommendation | |
| WebIDL | Editor's Draft 1.96 | |
| HTTP | Tentative (no validation) | 
The current implementation assumes that there are following requirements:
html element in http://www.w3.org/1999/xhtml
namespace is allowed to be a root element by the HTML5
specification.HTML5 is partially implemented.
In addition, the current implementation assumes that there are following requirements:
These definitions are updated version of their original definitions in previous versions of HTML (i.e. HTML 2.x, HTML4, Web Forms 2.0, or early drafts of HTML5).
For each row in the table below, if an attribute (i.e. an
  Attr node) met the following conditions, then the
  value attribute value of the node MUST
  be valid with regard to the constraints shown in the Value
  cell of the row.  The conditions are:
    
Element node
    pointed by the ownerElement attribute of the 
    Attr node).
    namespaceURI attribute value of the owner element
    is http://www.w3.org/1999/xhtml.
    manakaiLocalName attribute value [@@ TODO: ref]
    of the owner element is equal to the value in the Elementcell of the row.
namespaceURI attribute value of the Attr
    node is null.
    manakaiLocalName attribute value of the
    Attr node is equal to the value in the Attributecell of the row.
| Element | Attribute | Value | 
|---|---|---|
body | background
   | Syntactically same as img src [HTML5]
   | 
img | longdesc
   | Syntactically same as img src [HTML5]
   | 
input | accept-charset
   | Same as accept-charset attribute of the
  form element [HTML5]
   | 
input (type attribute is in Image Button
  state)
   | usemap
   | Syntactically same as img usemap [HTML5]
  
   | 
object | classid or codebase
   | Syntactically same as img src [HTML5]
   | 
head | profile
   | Same as a ping [HTML5]
  
   | 
object | archive
   | Same as a ping [HTML5]
   | 
object | codetype
   | Same as object type [HTML5]
   | 
param | type
   | Same as object type [HTML5]
   | 
address, div, h1,
  h2, h3, h4, h5,
  h6, or p
   | align
   | Enumerated attribute [HTML5] | 
img or object | align
   | Enumerated attribute [HTML5] | 
input (type attribute is in
  Image Button state)
   | align
   | Enumerated attribute [HTML5], where keywords are: top,
  middle, bottom, left,
  right
   | 
br | clear
   | Enumerated attribute [HTML5] | 
param | valuetype
   | Enumerated attribute [HTML5] | 
pre | width
   | Valid non-negative integer [HTML5] | 
ul, ol, dir,
  menu, or dl | compact
   | Boolean attribute [HTML5] | 
input (type attribute is in Image
  Button state)
   | ismap
   | Boolean attribute [HTML5] | 
table | frame or rules
   | Enumerated attribute [HTML5] | 
td | scope
   | Same as scope attribute of the th element
  [HTML5]
   | 
tbody, thead, tfoot,
  colgroup, col, tr, td,
  or th | align or valign
   | Enumerated attribute [HTML5] | 
form
   | replace
   | Enumerated attribute [HTML5] | 
input (type attribute is in
  Image Button or Submit Button state)
   | ||
button
   | ||
link | target
   | Valid browsing context name or keyword [HTML5] | 
meta | schema
   | Any string | 
a or link | rev
   | Unordered set of unique space-separated tokens [HTML5] (where any word is allowed) | 
table
   | cellpadding
   | A non-negative integer [HTML5] or a non-negative integer
  [HTML5] followed by a % character
   | 
cellspacing
   | ||
a
   | charset
   | Same as script charset [HTML5],
  syntactically
   | 
link
 | ||
textarea | pattern
 | Same as input pattern.
 | 
form | accept
 | Same as input accept.
   | 
version attribute of an html element.
| Element | Content Model | Allowed Context | 
|---|---|---|
center
   | Same as div [HTML5]
   | |
For an input element whose type attribute
is add, remove, move-up, or
move-down (ASCII case-insensitive) [WF2],
attributes that is not allowed for an input element whose
type attribute is in the Button state MUST NOT be specified.
The inputmode attribute applies to an
input element in Text, E-mail, URL, or Password state.  The replace attribute applies to an
input element in Image Button or Submit Button state.
The usemap attribute applies to an input
element in Image Button state.  The align attribute applies to an
input element in Image Button state. Any of these attributes MUST NOT be
specified for an input element whose type
attribute is in a state where the attribute does not apply.
The cache manifest syntax is also supported.
Atom 1.0 and Atom Threading 1.0 are supported.
However, conformance to some SHOULD-level requirements, as well as some informational guidelines, are currently not checked. In addition, whether an email-address or a Base64 encoding is correct or not is not checked either.
Use of XML digital signature and encryption is not supported.
The current implementation assumes that there are following requirements:
CSS @namespace and Selectors Level 3 are fully implemented.
Most of CSS 2.1 ( Candidate Recommendation) is implemented.
Most of CSS Color Module Level 3 ( Last Call Working Draft) is implemented.
Since the CSS 2.1 specification is sometimes ambigious or disagree with browsers, our implementation is tend to copy what browsers do unless there is strong resaon to do different thing.
In addition, the current implementation assumes that there are following requirements:
charset parameter of the media 
type text/css MUST be treated as if it 
were an unknown parameter for the purpose of determining styling langauge for 
an HTML style element.style 
element whose content is interpreted as a CSS style sheet 
MUST consist of zero or more 
text nodes.
Note that it may also contain zero or more comment and/or processing 
instruction nodes.Regular expression defined in ECMAScript Third Edition Section 15.10.1 is implemented, with the addition of the support for obsolete octal escape notation commonly supported by Web browsers.
To identify ECMAScript regular expressions, the Internet Media Type
text/x-regexp-js
is used.
WebIDL Editor's Draft revision 1.96 () is implemented.