AX_TEXT_04 incorrectly flags non-linked anchors

[karlgroves]

The following code was flagged in accessibility developer tools 2.10.9 with the message "The purpose of each link should be clear from the link text"

<a name="mainNavigation" class="skip-link"></a>

Per W3C documentation, the various accessibility APIs only expose link-related roles when the anchor element has an href attribute. Otherwise they assign a text-related role http://www.w3.org/TR/html-aam-1.0/

Recommendation: Modify AX_TEXT_04 so that it only checks anchor elements with the href attribute.