Should the rule imagebutton_alt_exists contain the label check (label as parent or label for attribute)?

[shunguoy]

There are couple of issues:

1. The rule currently doesn't check the label. For example,

<label for="GoBtn2">Go2</label>
<input type="image" name="Go2" id="GoBtn2" src="../support/btn_go.gif">

reports an error: The element of type "image" has no text alternative.

2. does the image inside an input element need a separate check?

<label for="GoBtn3">Go3</label>
<button id="GoBtn3"><img src="../support/btn_go.gif"></button>

reports an error: The image has neither an accessible name nor is marked as decorative or redundant

test case: test/v2/checker/accessibility/rules/imagebutton_alt_exists_ruleunit/InputImg-hasNoAlt.html

Also note, in the test case, for an image button (input with type=image), "The element's [value] attribute must be omitted", however, Chrome doesn't omit the value as shown in the test case.

[shunguoy]

Triage: the alt is reuqired for the input type='image' and displayed on screen, otherwise, the default value is "Submit".