A little help with API for plugins

Hi there,

Due to lack of crescendo/diminuendo (decrescendo) support in core I was using plugin to achieve that functionality.
However, I found current plugin too limited so was wondering of doing my own. I think I figured out how to use that Javascript thing. My problem is that I am not too familiar with built-in objects so don't know where to start so asking for a little help. I am looking for some kind of object, collection, property, method, whatever to access lines for crescendos/diminuendos. Idea is to traverse entire score in search for those lines, figure out their anchored chords and set up velocities. Approach would be completely the same as with existing plugin, just without the limitations like only one voice, one staff and need to do selection. So if someone can, please, direct me in right direction it would be much appreciated. Many thanks in advance.