The literary arts are full of structured strings. The main problem there is finding ones which have sufficiently interesting structure. E.g.
play ::= act+
act ::= scene+
scene ::= (stage-direction | line)+
stage-direction ::= "Enter" actor+ | "Exit" actor+
...
Gypsy Spellweaver helpfully points out that this can be elaborated to incorporate even more structure as
play ::= act ( act* [intermission act+] )*
although you may want to distinguish between play (the text) and play-performance (which may have intermissions) and use that as an illustration of sharing rules between grammars.
