Lex adds colors according to lexical categories. Typecheck verifies typing, and memorizes to let one see an expression's type by double-clicking on it. This is also valid for interfaces. If an error occurs, the part of the interface preceding the error is computed. After typechecking, pressing the right button pops up a menu giving the type of the pointed expression, and eventually allowing to follow some links.
Clear errors dismisses type-checker error messages and warnings.
The executed subshell is given the current load path. File use a source file or load a bytecode file. You may also import the browser's path into the subprocess. Signal C-c interrupts, and you can also kill the subprocess.