Wednesday 31 August 2016

forms - What's the proper value for a checked attribute of an HTML checkbox?



We all know how to form a checkbox input in HTML:






What I don't know -- what's the technically correct value for a checked checkbox? I've seen these all work:














Is the answer that it doesn't matter? I see no evidence for the answer marked as correct here from the spec itself:




Checkboxes (and radio buttons) are on/off switches that may be toggled
by the user. A switch is "on" when the control element's checked
attribute is set. When a form is submitted, only "on" checkbox
controls can become successful. Several checkboxes in a form may share
the same control name. Thus, for example, checkboxes allow users to
select several values for the same property. The INPUT element is used
to create a checkbox control.




What would a spec writer say is the correct answer? Please provide evidence-based answers.


Answer



Strictly speaking, you should put something that makes sense - according to the spec here, the most correct version is:






For HTML, you can also use the empty attribute syntax, checked="", or even simply checked (for stricter XHTML, this is not supported).



Effectively, however, most browsers will support just about any value between the quotes. All of the following will be checked:










And only the following will be unchecked:






See also this similar question on disabled="disabled".


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