I just saw a (very...) common question on SO, so I copied an answer from the PHP documentation with link.
Trouble is, I misremembered what the example did (remove excess whitespace vs. removing all whitespace as the poster had requested), and didn't notice this until a couple of commenters went, "Hey! WTF!" There's a moral in here somewhere about the dangers of copy+paste.
Is it appropriate in this situation to edit the answer with a remark to this effect? I don't want the incorrect version floating around there to mislead people who don't look at it too closely, but it also seems kind of... I dunno... unfair to the commenters (because I can just picture future commenters saying, "You guys are wrong! It clearly removes all whitespace!").