Consider default value "#top" for data.footer.top.href

[Andrew Duthie]

The default configuration provided for data.footer.top.href assigns a value of # to use as the href for the "Back to Top" link:

uswds-jekyll/_data/footer.yml

Lines 8 to 13 in 472991d

 # Configuration for "Return to top" link. 
 # Customize with 'text' and 'href' properties. 
 # Comment out to the following section to hide. 
 top: 
   text: Return to top 
   href: '#' 

As observed at 18F/development-guide#172 (and previously addressed at 18F/development-guide#130), this can cause errors to be flagged when using html-proofer, since it marks these fragments as invalid (see also gjtorikian/html-proofer#118).

An enhancement to html-proofer to allow #top fragment was proposed at gjtorikian/html-proofer#421 by @afeld and subsequently merged. As noted there, #top is a valid indicator for "top of the document". Since it's considered valid both by the HTML specification and by html-proofer, it may be a more sensible default to provide in this configuration.

[Greg Walker]

Closing as stale, on the assumption that the need will resurface if it still exists.