Variables in Default/Main.sublime-menu

[cheelam]

Following are the variables found in Default/Main.sublime-menu:
$file_types
$dictionaries
$build_systems
$macros
$packages
$platform

• What are they? Special pre-defined variables in Sublime Text? Any more of these variables out there?
• How their values being populated in Sublime Text?
• Can we introduce custom variables inside Sublime Text resource files (e.g. *.sublime-menu file). If yes, how can we set values on those custom variables?

[kingkeith]

What are they? Special pre-defined variables in Sublime Text?

Yes

Can we introduce custom variables inside Sublime Text resource files (e.g. *.sublime-menu file)

No, vote for this feature here:

Issue: Ability to create user defined $variables to be used in menu files.