what is the meaning of "cls" abbreviation ("cls tree")

Hi, in the intellij source code there are a bunch of classes that start with "Cls", for example:

com.intellij.psi.impl.compiled.ClsElementImpl
com.intellij.psi.impl.compiled.ClsEnumConstantImpl
com.intellij.psi.impl.compiled.ClsFieldImpl
etc.

These are used to create what's called the "cls tree".

My question is - what does "cls" mean here?  Does it just mean "class"?  Or is it an abbreviation for something the compiler is doing?

thank you very much - Matt