While perusing some I6 functions generated by I7, I saw some code that seems like it might be checking for ZSCII code 10. The DM4’s Table 2A on page 519 (online: DM4 Tables) has no entry for a code 10.
The code in question was generated for Glulx in a routine called TEXT_TY_BlobAccessI. Is there some special significance for that code in Glulx?