The default behavior of WordPress is to pull the union of multiple categories rather than the intersection. So, for example,
?cat=3,4 will show all items tagged to categories three and four. I think most people would expect this to be the reverse.
iSusi from Korea has a nice little plugin to fix this. InterCat sets the default behavior to generate, without additional joins, intersected category lists. Great for using WordPress to publish select streams of data to different sites.
Also of note: Olivier Crête’s Intersect Plugin
Following-up my post [cref 69], here’s what I used it for:
This is an excellent way to find a chunk of HTML with regex. It finds specific table rows containing either “String1” or “String2”, regardless of linefeeds, carriage returns, or other nefarious forms of whitespace.
Adapted from one of the more simple incarnations in Steve Levithan’s post about evolving a regex to find innermost HTML elements. Could be more complete and/or efficient.. but at least this one is fairly easy (kinda) to understand.