MacVim output question

in some documents I open in MacVim I get >> next to my line numbers and I can't find out what the meaning is.

I have janus installed and probably it is one of 开发者_运维技巧the plugins.

Thanks for any hint.

I guess it is syntastic plugin :

Syntastic is a syntax checking plugin that runs buffers through external syntax checkers as they are saved and opened. If syntax errors are detected, the user is notified and is happy because they didn't have to compile their code or execute their script to find them.

It comes with a list of syntax checkers which "just" wraps tools like tidy for xhtml...