In an attempt to not re-invent the wheel, I've been working on a CMS's text-sanitization layer. I found that SimplePie had a really good one in use with it's RSS feed, but it had a lot of features that I didn't need (such as image cache-ing, making relative urls absolute, etc.) so the actual amount of code that I'm using that's more-or-less a direct copy of SimplePie's code, is maybe 20-30% of the original
SimplePie_Sanitize class code.
My question is, since it's not exactly a direct copy (agree'd there are parts that are, and parts that aren't as I had to bring it up to PHP 5.3.6 spec and what-not), how much of the code has to be a direct copy for the BSD license (which SimplePie uses) to apply?
Keep in mind I'm going to be adding some of my own things into the code as well to help prevent XSS attacks so the class will eventually may only be 50% original, and 50% of the copied (or at least, the 20-30% that's left of it).
With that: is a simple 'THIS HAS CODE FROM THIS PROJECT' disclaimer enough, or do I have to apply the BSD license to the entire code file?