<quote>

Before adjacent strings get concatenated, a string can't be longer than 16380 single-byte characters.

A Unicode string of about one half this length would also generate this error.

</quote>

The solution apparently is to dice the string up into separate quoted chunks, i.e. instead of doing :-

"this is a \

very long \

string"

We need to do :-

"this is a "

"very long "

"string"