I am not an lhoward and I do not play one on TV, but I can explain that bit of regex.

lhoward has defined a set, as indicated by the [ ]. When perl's regex engine sees this, anything within the brackets will be considered a match. However, lhoward was tricky and made the first character a ^. When the first character of set is a ^, it negates the set ( mathematicians call it the complement, but I can't spell 'complement' ) and tells the regex to match everything but what is in the set.

[^<>]
[download]

is saying to match anything that isn't a < or a >

HTH,
mikfire