Commands which change output generally look like
\override Voice.Stem #'thickness = #3.0
This means that we must determine these bits of information:
Voice
.
Stem
.
thickness
.
3.0
.
Some tweakable options are called “subproperties” and reside inside properties. To tweak those, use commands in the form
\override Stem #'details #'beamed-lengths = #'(4 4 3)
We demonstrate how to glean this information from the notation manual and the program reference.
This page is for LilyPond-2.10.13 (stable-branch).