This {{WPBannerMeta}} subtemplate decides whether the banner instance is on the main templatepage, that is, whether the banner should display in its 'demo' version with all options demonstrated. It performs two checks

Is the page the
BANNER_NAME or subpage?
No Yes No Yes
and and not
Is category=no set? No yes yes
Yes
  1. Is the pagename the |BANNER_NAME=, or is the page a subpage of that page?
  2. Is the |category=no parameter set?

And then combines them together either with "and" (default) or another logical operator, eg "or"; this can be specified in the first unnamed parameter.