If this is based on 5e, won't the two classes each have their own tabs for spellcasting? So different expressions can be set up for each one?
Code:
class.cleric & (val:Level >= 1) & (val:Level <= 2)
is how I'd write the tag expression for this - it's about the same at low levels, but at high levels, it's lots less typing to say <= 9 than to include every tag from 1-9.