sparql lateral keyword

[SimonBin]

This is an experimental feature added by jena https://jena.apache.org/documentation/query/lateral-join.html @afs

I'm not sure how to best go about it (maybe would need a separate copy of the standard and an extension flag?)

but the yasqe editor is used also inside jena and it would be nice to avoid the syntax error while testing this experimental feature

[afs]

Also in Oxigraph.