What values for checked and selected are false

Question

I think according to W3 spec  you re supposed to do   lt input type  checkbox  checked  checked    gt    And   selected  selected    But  most browsers will accept it you just write  CHECKED  and don t give it a value  So  what if you do include the attribute  are there any values that would be  consistently  considered false

User · Accepted Answer

There are no values that will cause the checkbox to be unchecked  If the checked attribute exists  the checkbox will be checked regardless of what value you set it to    x000D   x000D   lt input type  checkbox  checked   gt  x000D   lt input type  checkbox  checked      gt  x000D   lt input type  checkbox  checked  checked    gt  x000D   lt input type  checkbox  checked  unchecked    gt  x000D   lt input type  checkbox  checked  true    gt  x000D   lt input type  checkbox  checked  false    gt  x000D   lt input type  checkbox  checked  on    gt  x000D   lt input type  checkbox  checked  off    gt  x000D   lt input type  checkbox  checked  1    gt  x000D   lt input type  checkbox  checked  0    gt  x000D   lt input type  checkbox  checked  yes    gt  x000D   lt input type  checkbox  checked  no    gt  x000D   lt input type  checkbox  checked  y    gt  x000D   lt input type  checkbox  checked  n    gt  x000D   x000D   x000D    Renders everything checked in all modern browsers  FF3 6  Chrome 10  IE8

User · Answer

No value is considered false  only the absence of the attribute  There are plenty of invalid values though  and some implementations might consider certain invalid values as false  HTML5 spec http   www w3 org TR html5 forms html attr-input-checked    The disabled content attribute is a boolean attribute   http   www w3 org TR html5 infrastructure html boolean-attributes    The presence of a boolean attribute on an element represents the true value  and the absence of the attribute represents the false value  If the attribute is present  its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute s canonical name  with no leading or trailing whitespace   Conclusion The following are valid  equivalent and true   lt input type  quot checkbox quot  checked   gt   lt input type  quot checkbox quot  checked  quot  quot    gt   lt input type  quot checkbox quot  checked  quot checked quot    gt   lt input type  quot checkbox quot  checked  quot ChEcKeD quot    gt   The following are invalid   lt input type  quot checkbox quot  checked  quot 0 quot    gt   lt input type  quot checkbox quot  checked  quot 1 quot    gt   lt input type  quot checkbox quot  checked  quot false quot    gt   lt input type  quot checkbox quot  checked  quot true quot    gt   The absence of the attribute is the only valid syntax for false   lt input type  quot checkbox quot    gt   Recommendation If you care about writing valid XHTML  use checked  quot checked quot   since  lt input checked gt  is invalid and other alternatives are less readable  Else  just use  lt input checked gt  as it is shorter

User · Answer

The checked and selected attributes are allowed only two values  which are a copy of the attribute name and  from HTML 5 onwards  an empty string  Giving any other value is an error   If you don t want to set the attribute  then the entire attribute must be omitted   Note that in HTML 4 you may omit everything except the value  HTML 5 changed this to omit everything except the name  which makes no practical difference    Thus  the complete  aside from variations in cAsE  set of valid representations of the attribute are    lt input     checked  checked  gt   lt  -- All versions of HTML   XHTML -- gt   lt input              checked  gt   lt  -- Only HTML 4 01 and earlier -- gt   lt input     checked           gt   lt  -- Only HTML 5 and later -- gt   lt input     checked           gt   lt  -- Only HTML 5 and later -- gt    Documents served as text html  HTML or XHTML  will be fed through a tag soup parser  and the presence of a checked attribute  with any value  will be treated as  This element should be checked   Thus  while invalid  checked  true   checked  yes   and checked  false  will all trigger the checked state   I ve not had any inclination to find out what error recovery mechanisms are in place for XML parsing mode should a different value be given to the attribute  but I would expect that the legacy of HTML and or simple error recovery would treat it in the same way  If the attribute is there then the element is checked    And all the above applies equally to selected as it does to checked

User · Answer

The empty string is false as a rule   Apparently the empty string is not respected as empty in all browsers and the presence of the checked attribute is taken to mean checked   So the entire attribute must either be present or omitted

User · Answer

Actually  the HTML 4 01 spec says that these attributes do not require values  I haven t personally encountered a situation where providing a value rendered these controls as unselected   Here are the respective links to the spec document for selected and checked   Edit  Firebug renders the checkbox as checked regardless of any values I put in quotes for the checked attribute  including just typing  checked  with no values whatsoever   and IE 8 s Developer Tools forces checked  checked   I m not sure if any similar tools exist for other browsers that might alter the rendered state of a checkbox  however

[html] What values for checked and selected are false?

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