I'm following the Simple Language development tutorial, and I'm at the section on adding an annotator. It requires the class PsiLiteralExpression, but, I can't seem to get the symbol to resolve. I am importing com.intellij.psi.*, which in theory should contain the PsiLiteralExpression class, but it seems that it does not, in fact contain it. I'm not sure if I just don't have my Platform SDK set up properly, or what, but, I set that up by following the Setting Up a Development Environment page, so I don't think it should have any problems... The problem exists when I open the completed Simple Language Project from the sdk docs repo, as well, so it is not exclusive to the version of the project that I am working through.
Thanks in advance for your help.