What's the proper value for a checked attribute of an HTML checkbox?
We all know how to form a checkbox input in HTML:
<input name="checkbox_name" id="checkbox_id" type="checkbox">
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:
<input name=name id=id type=checkbox checked=checked>
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:
<input name=name id=id type=checkbox checked>
<input name=name id=id type=checkbox checked="">
<input name=name id=id type=checkbox checked="yes">
<input name=name id=id type=checkbox checked="blue">
<input name=name id=id type=checkbox checked="false">
And only the following will be unchecked:
<input name=name id=id type=checkbox>
See also this similar question on disabled="disabled".