Considering that the unranked tree languages L(G) and L(G′) are those defined by given non-recursive 
XML types G and G′, this paper proposes a simple and intuitive method to verify whether L(G) is 
“approximatively” included in L(G′). Our approximative criterion consists in weakening the 
father-children relationships. Experimental results are discussed, showing the efficiency of our 
method in many situations.