Minecraft wiki entry for Target_selectors, associated text: Examples in Bedrock Edition:
@e[x=1,dx=4,y=2,dy=5,z=3,dz=6] — Select all entities whose feet are within the block region (1~5, 2~7, 3~9).
@e[x=1,y=2,z=3,dx=0,dy=0,dz=0] — Select all entities whose feet contains the point (1, 2, 3).