if doc.mmodules.has(mmodule) then mmodules.add mmodule
# collect mclasses
for mclass in mmodule.intro_mclasses do
if doc.mclasses.has(mclass) then intros.add mclass
end
if doc.mmodules.has(mmodule) then mmodules.add mmodule
# collect mclasses
for mclass in mmodule.intro_mclasses do
if doc.mclasses.has(mclass) then intros.add mclass
end