HTML Living Standard Web Standard

The HTML Living Standard describes the behavior of HTML elements and attributes. It is continuously maintained and supersedes HTML4, XHTML1, DOM Level 2 HTML, and all previous HTML specifications, and is is often called HTML5.

• HTML Living Standard

Rules

• bdo must have a dir attribute
• label elements may not contain multiple form controls
• for must refer to a non-hidden form control
• section must not appear inside address
• nav must not appear inside address
• article must not appear inside address
• aside must not appear inside address
• footer must not appear inside header element
• footer must not appear inside footer element
• footer must not appear inside address element
• h1 must not appear inside address
• h2 must not appear inside address
• h3 must not appear inside address
• h4 must not appear inside address
• h5 must not appear inside address
• h6 must not appear inside address
• header must not appear inside footer
• header must not appear inside address
• header must not appear inside header
• table must not appear inside caption
• summary is obsolete
• a cannot have clickable ancestor a
• details cannot have clickable ancestor a
• embed cannot have clickable ancestor a
• iframe cannot have clickable ancestor a
• label cannot have clickable ancestor a
• a cannot have clickable ancestor button
• details cannot have clickable ancestor button
• embed cannot have clickable ancestor button
• iframe cannot have clickable ancestor button
• label cannot have clickable ancestor button
• button cannot have clickable ancestor a
• textarea cannot have clickable ancestor a
• select cannot have clickable ancestor a
• input cannot have clickable ancestor a
• button cannot have clickable ancestor button
• textarea cannot have clickable ancestor button
• select cannot have clickable ancestor button
• input cannot have clickable ancestor button
• button inside label with for must have an id matching for
• textarea inside label with for must have an id matching for
• select inside label with for must have an id matching for
• input inside label with for must have an id matching for
• video with controls must not appear as a descendant of a
• audio with controls must not appear as a descendant of a
• video with controls must not appear as a descendant of button
• audio with controls must not appear as a descendant of button
• menu with type=toolbar must not appear inside a
• menu with type=toolbar must not appear inside button
• img with usemap must not appear inside a
• img with usemap must not appear inside button
• object with usemap must not appear inside a
• object with usemap must not appear inside button
• area must be inside a map element
• img with ismap must be inside an a element with an href
• list attribute must refer to a datalist element
• input type=button must not have empty value attribute
• label attribute must not be empty
• default attribute can only appear on one track inside audio or video
• id on a map element must be identical to the name attribute
• Multiple selected options only allowed when select has multiple attribute
• select with required must contain an option element
• First option in a required select dropdown must have an empty value or empty text content
• language=JavaScript can only be used with type='text/javascript'
• script cannot have attribute charset unless src is specified
• script cannot have attribute defer unless src is specified
• script cannot have attribute async unless src or type=module is specified
• progress must not appear inside another progress element
• Progress value must not be greater than max
• Progress value must not be greater than 1.0
• meter must not appear inside another meter element
• min must not be greater than value
• value must be greater than or equal to 0 if min not specified
• value must not be greater than max
• value must be less than or equal to 1 if max not specified
• min must not be greater than max
• max must be greater than or equal to 0 if min not specified
• min must be less than or equal to 1 if max not specified
• min must not be greater than low
• low must be greater than or equal to 0 if min not specified
• min must not be greater than high
• high must be greater than or equal to 0 if min not specified
• low must not be greater than high
• high must not be greater than max
• high must be less than or equal to 1 if max not specified
• low must not be greater than max
• low must be less than or equal to 1 if max not specified
• min must not be greater than optimum
• optimum must be greater than or equal to 0 if min not specified
• optimum must not be greater than max
• optimum must be less than or equal to 1 if max not specified
• acronym is obsolete
• applet is obsolete
• center is obsolete
• font is obsolete
• big is obsolete
• strike is obsolete
• tt is obsolete
• basefont is obsolete
• dir is obsolete
• frameset is obsolete
• noframes is obsolete
• coords on a is obsolete
• shape on a is obsolete
• urn on a is obsolete
• charset on a is obsolete
• methods on a is obsolete
• target on link is obsolete
• urn on link is obsolete
• charset on link is obsolete
• methods on link is obsolete
• nohref on area is obsolete
• name on embed is obsolete
• profile on head is obsolete
• version on html is obsolete
• name on img is obsolete
• usemap on input is obsolete
• type on the li element is obsolete
• type on the ul element is obsolete
• scheme on meta is obsolete
• meta http-equiv=content-language is obsolete
• archive on object is obsolete
• classid on object is obsolete
• code on object is obsolete
• codebase on object is obsolete
• codetype on object is obsolete
• declare on object is obsolete
• standby on object is obsolete
• name on option is obsolete
• type on param is obsolete
• valuetype on param is obsolete
• language on script is obsolete
• scope on td is obsolete
• abbr on td is obsolete
• axis on td is obsolete
• axis on th is obsolete
• align on caption is obsolete
• align on iframe is obsolete
• align on img is obsolete
• align on input is obsolete
• align on object is obsolete
• align on embed is obsolete
• align on legend is obsolete
• align on table is obsolete
• align on hr is obsolete
• align on div is obsolete
• align on h1 is obsolete
• align on h2 is obsolete
• align on h3 is obsolete
• align on h4 is obsolete
• align on h5 is obsolete
• align on h6 is obsolete
• align on p is obsolete
• align on col is obsolete
• align on colgroup is obsolete
• align on tbody is obsolete
• align on td is obsolete
• align on tfoot is obsolete
• align on th is obsolete
• align on thead is obsolete
• align on tr is obsolete
• width on col is obsolete
• width on colgroup is obsolete
• width on hr is obsolete
• width on pre is obsolete
• width on table is obsolete
• width on td is obsolete
• width on th is obsolete
• char on col is obsolete
• char on colgroup is obsolete
• char on tbody is obsolete
• char on td is obsolete
• char on tfoot is obsolete
• char on th is obsolete
• char on thead is obsolete
• char on tr is obsolete
• charoff on col is obsolete
• charoff on colgroup is obsolete
• charoff on tbody is obsolete
• charoff on td is obsolete
• charoff on tfoot is obsolete
• charoff on th is obsolete
• charoff on thead is obsolete
• charoff on tr is obsolete
• valign on col is obsolete
• valign on colgroup is obsolete
• valign on tbody is obsolete
• valign on td is obsolete
• valign on tfoot is obsolete
• valign on th is obsolete
• valign on thead is obsolete
• valign on tr is obsolete
• alink on body is obsolete
• background on body is obsolete
• bgcolor on body is obsolete
• link on body is obsolete
• bottommargin on body is obsolete
• marginheight on the body element is obsolete
• leftmargin on body is obsolete
• rightmargin on body is obsolete
• topmargin on the body element is obsolete
• marginwidth on the body element is obsolete
• text on body is obsolete
• vlink on body is obsolete
• clear on br is obsolete
• hspace on embed is obsolete
• vspace on embed is obsolete
• noshade on the hr element is obsolete
• size on the hr element is obsolete
• color on the hr element is obsolete
• compact on the dl element is obsolete
• compact on the menu element is obsolete
• compact on the ol element is obsolete
• compact on the ul element is obsolete
• allowtransparency on iframe is obsolete
• frameborder on iframe is obsolete
• marginheight on iframe is obsolete
• marginwidth on iframe is obsolete
• scrolling on iframe is obsolete
• hspace on the img element is obsolete
• hspace on the object element is obsolete
• vspace on the img element is obsolete
• vspace on the object element is obsolete
• border on the img element is obsolete
• border on the object element is obsolete
• bgcolor on the table element is obsolete
• border on the table element is obsolete
• cellpadding on the table element is obsolete
• cellspacing on the table element is obsolete
• frame on the table element is obsolete
• rules on the table element is obsolete
• bgcolor on the td element is obsolete
• bgcolor on the th element is obsolete
• height on the td element is obsolete
• height on the th element is obsolete
• nowrap on the td element is obsolete
• nowrap on the th element is obsolete
• bgcolor on the tr element is obsolete
• xml:lang requires lang with same value to be present
• border on img element is obsolete
• language on the script element is obsolete
• name on the a element is obsolete
• video element has more than one default track
• audio element has more than one default track
• form cannot have ancestor form
• progress cannot have ancestor progress
• meter cannot have ancestor meter
• dfn cannot have ancestor dfn
• noscript cannot have ancestor noscript
• label cannot have ancestor label
• address cannot have ancestor address
• section cannot have ancestor address
• nav cannot have ancestor address
• article cannot have ancestor address
• header cannot have ancestor header
• header cannot have ancestor footer
• header cannot have ancestor address
• footer cannot have ancestor header
• footer cannot have ancestor footer
• header cannot have ancestor dt
• footer cannot have ancestor dt
• article cannot have ancestor dt
• nav cannot have ancestor dt
• section cannot have ancestor dt
• h1 cannot have ancestor dt
• h2 cannot have ancestor dt
• h3 cannot have ancestor dt
• h4 cannot have ancestor dt
• h5 cannot have ancestor dt
• h6 cannot have ancestor dt
• hgroup cannot have ancestor dt
• header cannot have ancestor th
• footer cannot have ancestor th
• article cannot have ancestor th
• nav cannot have ancestor th
• section cannot have ancestor th
• h1 cannot have ancestor th
• h2 cannot have ancestor th
• h3 cannot have ancestor th
• h4 cannot have ancestor th
• h5 cannot have ancestor th
• h6 cannot have ancestor th
• hgroup cannot have ancestor th
• footer cannot have ancestor address
• h1 cannot have ancestor address
• h2 cannot have ancestor address
• h3 cannot have ancestor address
• h4 cannot have ancestor address
• h5 cannot have ancestor address
• h6 cannot have ancestor address
• table cannot have ancestor caption
• a cannot have ancestor a
• a cannot have ancestor button
• button cannot have ancestor a
• button cannot have ancestor button
• details cannot have ancestor a
• details cannot have ancestor button
• dialog cannot have ancestor a
• dialog cannot have ancestor button
• embed cannot have ancestor a
• embed cannot have ancestor button
• iframe cannot have ancestor a
• iframe cannot have ancestor button
• label cannot have ancestor a
• label cannot have ancestor button
• select cannot have ancestor a
• select cannot have ancestor button
• textarea cannot have ancestor a
• textarea cannot have ancestor button
• main cannot have ancestor a
• main cannot have ancestor address
• main cannot have ancestor article
• main cannot have ancestor aside
• main cannot have ancestor audio
• main cannot have ancestor blockquote
• main cannot have ancestor canvas
• main cannot have ancestor caption
• main cannot have ancestor dd
• main cannot have ancestor del
• main cannot have ancestor details
• main cannot have ancestor dialog
• main cannot have ancestor dt
• main cannot have ancestor fieldset
• main cannot have ancestor figure
• main cannot have ancestor footer
• main cannot have ancestor header
• main cannot have ancestor ins
• main cannot have ancestor li
• main cannot have ancestor main
• main cannot have ancestor map
• main cannot have ancestor nav
• main cannot have ancestor noscript
• main cannot have ancestor object
• main cannot have ancestor section
• main cannot have ancestor slot
• main cannot have ancestor td
• main cannot have ancestor th
• main cannot have ancestor video
• a cannot have ancestor with role=button
• a cannot have ancestor with role=link
• button cannot have ancestor with role=button
• button cannot have ancestor with role=link
• details cannot have ancestor with role=button
• details cannot have ancestor with role=link
• dialog cannot have ancestor with role=button
• dialog cannot have ancestor with role=link
• embed cannot have ancestor with role=button
• embed cannot have ancestor with role=link
• iframe cannot have ancestor with role=button
• iframe cannot have ancestor with role=link
• label cannot have ancestor with role=button
• label cannot have ancestor with role=link
• select cannot have ancestor with role=button
• select cannot have ancestor with role=link
• textarea cannot have ancestor with role=button
• textarea cannot have ancestor with role=link
• Element with tabindex cannot have ancestor with role=button
• Element with tabindex cannot have ancestor with role=link
• audio with controls cannot have ancestor with role=button
• audio with controls cannot have ancestor with role=link
• img with usemap cannot have ancestor with role=button
• img with usemap cannot have ancestor with role=link
• input cannot have ancestor with role=button
• input cannot have ancestor with role=link
• menu with toolbar cannot have ancestor with role=button
• menu with toolbar cannot have ancestor with role=link
• object with usemap cannot have ancestor with role=button
• object with usemap cannot have ancestor with role=link
• video with controls cannot have ancestor with role=button
• video with controls cannot have ancestor with role=link
• role=button cannot have ancestor with role=button
• role=button cannot have ancestor with role=link
• role=checkbox cannot have ancestor with role=button
• role=checkbox cannot have ancestor with role=link
• role=combobox cannot have ancestor with role=button
• role=combobox cannot have ancestor with role=link
• role=grid cannot have ancestor with role=button
• role=grid cannot have ancestor with role=link
• role=gridcell cannot have ancestor with role=button
• role=gridcell cannot have ancestor with role=link
• role=listbox cannot have ancestor with role=button
• role=listbox cannot have ancestor with role=link
• role=menu cannot have ancestor with role=button
• role=menu cannot have ancestor with role=link
• role=menubar cannot have ancestor with role=button
• role=menubar cannot have ancestor with role=link
• role=menuitem cannot have ancestor with role=button
• role=menuitem cannot have ancestor with role=link
• role=menuitemcheckbox cannot have ancestor with role=button
• role=menuitemcheckbox cannot have ancestor with role=link
• role=menuitemradio cannot have ancestor with role=button
• role=menuitemradio cannot have ancestor with role=link
• role=option cannot have ancestor with role=button
• role=option cannot have ancestor with role=link
• role=radio cannot have ancestor with role=button
• role=radio cannot have ancestor with role=link
• role=scrollbar cannot have ancestor with role=button
• role=scrollbar cannot have ancestor with role=link
• role=searchbox cannot have ancestor with role=button
• role=searchbox cannot have ancestor with role=link
• role=slider cannot have ancestor with role=button
• role=slider cannot have ancestor with role=link
• role=spinbutton cannot have ancestor with role=button
• role=spinbutton cannot have ancestor with role=link
• role=switch cannot have ancestor with role=button
• role=switch cannot have ancestor with role=link
• role=tab cannot have ancestor with role=button
• role=tab cannot have ancestor with role=link
• role=textbox cannot have ancestor with role=button
• role=textbox cannot have ancestor with role=link
• role=treeitem cannot have ancestor with role=button
• role=treeitem cannot have ancestor with role=link
• Element link not allowed in body
• role=cell must be owned by role=row
• role=option must be owned by role=listbox
• role=menuitem must be owned by role=menu or menubar
• role=menuitemcheckbox must be owned by role=menu or menubar
• role=menuitemradio must be owned by role=menu or menubar or group
• role=tab must be owned by role=tablist
• role=treeitem must be owned by role=tree or group
• role=listitem must be owned by role=list
• role=gridcell must be owned by role=row
• role=columnheader must be owned by role=row
• role=rowheader must be owned by role=row
• role=row must be owned by role=grid or rowgroup or treegrid or table
• role=rowgroup must be owned by role=grid or treegrid or table
• role=feed must contain role=article
• role=grid must contain role=row or rowgroup
• role=list must contain role=listitem
• role=listbox must contain role=option
• role=menu must contain role=menuitem or menuitemcheckbox or menuitemradio
• role=radiogroup must contain role=radio
• role=row must contain role=cell or columnheader or gridcell or rowheader
• role=rowgroup must contain role=row
• role=table must contain role=row or rowgroup
• role=tablist must contain role=tab
• role=tree must contain role=treeitem
• role=treegrid must contain role=row or rowgroup
• title must not be empty
• option element must not be empty
• usemap refers to non-existent map
• Autonomous custom elements must not use is
• Only utf-8 is allowed for form accept-charset
• Only utf-8 is allowed for meta charset
• Only utf-8 is allowed for script charset
• Only text/css is allowed for style type
• Use figcaption instead of table caption
• script with nomodule must not have type=module
• link scope can only be used with rel=serviceworker
• link updateviacache can only be used with rel=serviceworker
• link workertype can only be used with rel=serviceworker
• blocking can only be used with modulepreload, preload or stylesheet
• link color can only be used with rel=mask-icon
• link disabled can only be used with rel=stylesheet
• link fetchpriority can only be used with external resource types
• link must have href or imagesrcset
• link with imagesizes must have imagesrcset
• link with imagesizes must have as=image
• link with imagesrcset must have as=image
• link with imagesizes must have rel=preload
• link with imagesrcset must have rel=preload
• link sizes can only be used with rel=icon, rel=apple-touch-icon or rel=apple-touch-icon-precomposed
• link as only allowed with rel=preload or rel=modulepreload
• Alternate stylesheets must have a title
• link integrity can only be used with rel=stylesheet, rel=preload or rel=modulepreload
• script fetchpriority should only be used with src
• script with integrity attribute must have src
• script with type=module cannot have a defer attribute
• script with type=importmap cannot have src
• meta with media attribute must have name=theme-color
• Avoid meta viewports that prevent zooming
• Multiple meta elements with name=description
• Section lacks heading
• Article lacks heading
• Multiple meta charset elements
• Multiple meta elements with charset and content-type
• Multiple meta elements with http-equiv=content-type
• Page has multiple h1 elements
• Page has multiple main elements
• xml:lang without matching lang
• keygen is obsolete
• datafld is obsolete
• dataformatas is obsolete
• datasrc is obsolete
• datapagesize on table is obsolete
• longdesc on img is obsolete
• for attribute on script is obsolete
• event attribute on script element is obsolete
• itemid can only be used on elements with itemscope and itemtype
• itemref can only be used on elements with itemscope
• itemtype can only be used on elements with itemscope
• img with alt='' must not have role
• Page has multiple autofocus elements
• typemustmatch can only be used when data and type are specified
• img must have an alt attribute
• Broken aria-activedescendant ID reference
• Broken aria-controls ID reference
• Broken aria-describedby ID reference
• Broken aria-flowto ID reference
• Broken aria-labelledby ID reference
• Broken aria-owns ID reference
• Unsupported SVG version
• aria-hidden not allowed on base
• aria-hidden not allowed on col
• aria-hidden not allowed on colgroup
• aria-hidden not allowed on head
• aria-hidden not allowed on html
• aria-hidden not allowed on input with type=hidden
• aria-hidden not allowed on link
• aria-hidden not allowed on map
• aria-hidden not allowed on meta
• aria-hidden not allowed on noscript
• aria-hidden not allowed on param
• aria-hidden not allowed on script
• aria-hidden not allowed on slot
• aria-hidden not allowed on source
• aria-hidden not allowed on style
• aria-hidden not allowed on template
• aria-hidden not allowed on title
• aria-hidden not allowed on track
• aria- attributes are not allowed on input elements with type=hidden
• role=article unnecessary for article
• role=complementary unnecessary for aside
• role=document unnecessary for body
• role=button unnecessary for button
• role=listbox unnecessary for datalist
• role=definition unnecessary for dd
• role=group unnecessary for details
• role=term unnecessary for dfn
• role=dialog unnecessary for dialog
• role=term unnecessary for dt
• role=group unnecessary for fieldset
• role=figure unnecessary for figure
• role=contentinfo unnecessary for footer
• role=form unnecessary for form
• role=heading unnecessary for h1
• role=heading unnecessary for h2
• role=heading unnecessary for h3
• role=heading unnecessary for h4
• role=heading unnecessary for h5
• role=heading unnecessary for h6
• role=banner unnecessary for header
• role=separator unnecessary for hr
• role=listitem unnecessary for li
• role=link unnecessary for link
• role=main unnecessary for main
• role=math unnecessary for math
• role=navigation unnecessary for nav
• role=list unnecessary for ol
• role=option unnecessary for option
• role=status unnecessary for output
• role=progressbar unnecessary for progress
• role=region unnecessary for section
• role=listbox unnecessary for select
• role=button unnecessary for summary
• role=table unnecessary for table
• role=rowgroup unnecessary for tbody
• role=textbox unnecessary for textarea
• role=rowgroup unnecessary for tfoot
• role=rowgroup unnecessary for thead
• role=cell unnecessary for td
• role=row unnecessary for tr
• role=list unnecessary for ul
• role=columnheader unnecessary for th
• meter does not need a role
• optgroup does not need a role
• role=button unnecessary for input type=button
• role=checkbox unnecessary for input type=checkbox
• role=button unnecessary for input type=image
• role=spinbutton unnecessary for input type=number
• role=radio unnecessary for input type=radio
• role=slider unnecessary for input type=range
• role=button unnecessary for input type=reset
• role=button unnecessary for input type=submit
• role=button unnecessary for button type=menu
• role=toolbar unnecessary for menu type=toolbar
• role=textbox unnecessary for input type=email and no list attribute
• role=textbox unnecessary for input type=tel and no list attribute
• role=textbox unnecessary for input type=text and no list attribute
• role=searchbox unnecessary for input type=search and no list attribute
• role=textbox unnecessary for input type=url and no list attribute
• role=combobox unnecessary for input type=email and a list attribute
• role=combobox unnecessary for input type=tel and a list attribute
• role=combobox unnecessary for input type=text and a list attribute
• role=combobox unnecessary for input type=search and a list attribute
• role=combobox unnecessary for input type=url and a list attribute
• aria-haspopup should not be used on input type=email with a list attribute
• aria-haspopup should not be used on input type=tel with a list attribute
• aria-haspopup should not be used on input type=text with a list attribute
• aria-haspopup should not be used on input type=search with a list attribute
• aria-haspopup should not be used on input type=url with a list attribute
• role=listitem unnecessary for li inside ol or ul
• role=link unnecessary for a, area and link with href
• role=combobox unnecessary for select elements with size less than two
• role=listbox unnecessary for select with multiple or size greater than one
• Non-empty img alt used with role=none or role=presentation
• img with no alt cannot have a role
• img with no alt cannot have aria- attributes
• figure with a figcaption must not have a role
• role forbidden on td th and tr elements inside tables
• aria-colspan not needed with colspan
• aria-colspan must match colspan
• aria-disabled not needed with disabled
• aria-disabled=false cannot be used with disabled
• aria-hidden not needed with hidden
• aria-hidden=false cannot be used with hidden
• aria-readonly not needed with readonly
• aria-readonly=false cannot be used with readonly
• aria-required not needed with required
• aria-required=false cannot be used with required
• aria-rowspan not needed with rowspan
• aria-rowspan must match rowspan
• autocomplete only allowed with some input types
• list only allowed with some input types
• maxlength only allowed with some input types
• minlength only allowed with some input types
• pattern only allowed with some input types
• placeholder only allowed with some input types
• readonly only allowed with some input types
• required only allowed with some input types
• size only allowed with some input types
• aria-valuemax forbidden on progress with max attribute
• aria-valuemax redundant on progress
• aria-valuemax forbidden on meter with max attribute
• aria-valuemax redundant on meter
• aria-valuemin forbidden on meter with min attribute
• aria-valuemin redundant on meter
• aria-valuemax forbidden on input with max attribute
• aria-valuemax redundant on input
• aria-valuemin forbidden on input with min attribute
• aria-valuemin redundant on input
• aria-disabled=true should not be used on links
• aria-checked must not be used on input with type=radio or type=checkbox
• aria-multiselectable should not be used on select
• aria-selected should not be used on option
• aria-placeholder must not be used with placeholder
• aria-readonly=true must not be used with contenteditable
• ARIA label used on role that prohibits naming
• Focusable role=separator must have aria-valuenow
• ARIA error
• Missing ARIA attribute
• HTML parsing error
• HTML Validation Error
• HTML validation warning
• Unrecoverable parsing error
• Invalid language attribute
• ARIA role is invalid
• Invalid aria-controls value
• Autocomplete value is invalid
• Element caption not allowed here
• Element dd requires dl parent
• Element dt requires dl parent
• Element li requires ol or ul parent
• Element option requires select or optgroup parent
• Element summary requires details` parent
• img in noscript before body
• body seen when body already open