Plugin can access other plugins, behavior can access a plugin, too.
Worksheet plugin connects to a Timeline object in an action to get reference. So that worksheet object can call timeline's CreateTimer function.
Timer behavior is similar with worksheet, it connects to a timeline object, accesses timeline's function..
There are some other way to get the object(plugin) reference. Like -
a. Define a global function reference
b. Then get function reference
It's very interesting to design co-work plugins.