FWIW, I tried with LibXML but I can't get no results with these queries either

print for $dom->findnodes(q{ substring( //p/text() , 0, 4 ) });
print for $dom->findnodes(q{ substring(string(//title),1,4) });
print for $dom->findnodes(q{ substring(string(//title/text()),1,4) });
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