grammar is very important in comments.

One of these would make your point valid, as you have it, "below a..." you're saying there's something below a slightly modified version....

 "below, a slightly modified version of Patrick Gillespie's BBCode Parser to make it work like the bbcode on myanimelist, thank you for making this available"

OR

 "The below is a slightly modified version of Patrick Gillespie's BBCode Parser to make it work like the bbcode on myanimelist, thank you for making this available"



This is helpful not only for others, but doing this will save you plenty of head aches too.