Expressions for text style parameters

Usually I have little problems programming things with Expressions.
However, I can't get or set any of the "newer" accessible parameters like font size, tracking, leading, fill color, etc. etc.
This seems to take place with techniques that do not resemble normal After Effects expressions.
None of the examples that I can find on the entire internet work.

Something like

text.sourceText.style.setFontSize(25);

should work when pasted into the Source Text expression field, should it not?