Breaking lines at Grapheme Boundaries

[Richard Wordingham via Unicode]

If a renderer claims to support a writing system, should it render the
text reasonably if its client breaks lines at extended grapheme
cluster boundaries?

The writing system itself has no compunction about
breaking lines between legacy grapheme clusters, though I've no idea
how I should get a mere word-processor to implement some of these line
breaks.  (The big problem here is that Indic reordering would be
required around the line break.)

Richard.