iFrames usage is discouraged by WCAG

AFFECTS:

• xwiki:Main.WebHome (en, fr, ca, pt_BR)
• xwiki:Help.Videos.WebHome
• xwiki:FlamingoThemes.Cerulean
• xwiki:FlamingoThemes.Charcoal
• xwiki.FlamingoThemes.* (other 22 entries)
• xwiki:FlamingoThemesCode.ThemeSheet
• xwiki:FlamingoThemesCode.ThemeTemplate

ERROR:

• org.xwiki.test.webstandards.CustomDutchWebGuidelinesValidationTest.Validating HTML5 Dutch Web Guidelines validity for: xwiki:FlamingoThemes.Cerulean executed with credentials Admin:admin (from org.xwiki.test.webstandards.AllTests)
• ERROR: The use of iframes is not allowed.

INVALIDATES:

• Dutch Guidelines: validateRpd12s1()
  • https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-tools/xwiki-platform-tool-standards-validator/src/main/java/org/xwiki/validator/DutchWebGuidelinesValidator.java#L1180
• R-pd.12.1 "Do not use frames on websites. This applies to regular frames in framesets as well as iframes."

FIXES:

• VAR1: Remove the Homepage video
• VAR2: Make exceptions for Main.WebHome, Help.Videos and FlamingoThemes.*.
  • There is no other way except using iframes to embed YouTube videos. A solution would be to put images as placeholders and load with JS the video but that would fake it somehow, plus it's additional code that needs to be written.
  • But in the case of FlamingoThemes, the iframes are needed in order to have the Preview.