IsItAMask - Modo Python API example to show if the selected item is a texture layer mask or not.

IsItAMask.py

import lx
import lxu.select

scn_svc = lx.service.Scene()

def IsItAMask(item):   
    if scn_svc.ItemTypeName(scn_svc.ItemTypeSuper(item.Type())) == lx.symbol.sITYPE_TEXTURELAYER:
        scene = item.Context()
        graph = lx.object.ItemGraph(scene.GraphLookup(lx.symbol.sGRAPH_SHADELOC))
        if graph.RevCount(item) > 0:
            return True
        else:
            return False

for item in lxu.select.ItemSelection().current():
    if IsItAMask(item) == True:
        lx.out("%s: It's a mask" % item.UniqueName())
    else:
        lx.out("%s: It's not a mask" % item.UniqueName())