This HTML5 document contains 4 embedded RDF statements represented using HTML+Microdata notation.

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PrefixNamespace IRI
isaphttp://webisa.webdatacommons.org/prov/
isahttp://webisa.webdatacommons.org/
n5stackoverflow.
rdfhttp://www.w3.org/1999/02/22-rdf-syntax-ns#
provhttp://www.w3.org/ns/prov#
xsdhhttp://www.w3.org/2001/XMLSchema#
Subject Item
isa:186607588
rdf:type
prov:Entity
prov:value
So the choice between elements and attributes is more-or-less arbitrary except for things that can not be represented with attributes (see feenster's answer).
prov:wasQuotedFrom
n5:com
Subject Item
isap:334922555
prov:wasDerivedFrom
isa:186607588