Notifications' RSS feed link is using target attribute

AFFECTS:

• All pages
• xwiki:XWiki.WatchListRss
• xwiki:Main.WebHome
• etc.

ERROR:

• org.xwiki.test.webstandards.CustomDutchWebGuidelinesValidationTest.Validating HTML5 Dutch Web Guidelines validity for: xwiki:XWiki.WatchListRss executed with credentials Admin:admin (from org.xwiki.test.webstandards.AllTests)
• ERROR: There are links on this page that use the "target" attribute, this implies the opening of new windows. The "target" attribute has also been deprecated.

INVALIDATES:

• Dutch Guidelines: validateRpd8s14()
  • https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-tools/xwiki-platform-tool-standards-validator/src/main/java/org/xwiki/validator/DutchWebGuidelinesValidator.java#L910
• R-pd.8.14 "Links on websites should not automatically open new windows without warning."

EXPLANATION:

• Cause by usage of target='blank'
• The ERROR message is confusing, since target attribute is not deprecated, see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#Attributes
• Target invalidates also WCAG 2.1, see
  • https://www.w3.org/TR/WCAG20-TECHS/G200.html
  • https://www.w3.org/TR/WCAG20-TECHS/G201.html
  • the general recommendation is to have it only when absolutely necessary, and to provide warning modals before opening the link using JS or CSS. There are also some performance mentions that the new pages will open in the same browser tab process.
• https://css-tricks.com/use-target_blank/
• https://www.w3schools.com/tags/att_link_target.asp

FIXES:

• VAR1: Remove the target attribute
• VAR2: Add additional message / warning that the window will be opened in another tab
  • https://www.w3.org/TR/WCAG20-TECHS/H83.html