How to draw lines.How to draw lines.How to draw lines.
There is no line widget in the current version. You can add it from code after calling the ui_init().
Just out of curiosity, for which purpose do you want to use the line widget?
@kisvegabor Line widget would be really useful 
I needed line to display different “section” and I came up with this workaround 
All my lines are 2 px height panels.
You can also use a bottom border on the containers.