How do I solve 17 across in Daily Telegraph Cryptic 31236?

Question

Accepted Answer

17 across reads "Reserve position for material" (9 letters); the answer is SUBSTANCE. It's a charade: the answer breaks into parts in clue order, each part clued by a word or short phrase. No indicators needed; watch for standard abbreviations (RA = artist, US = American, IN = at home) and short synonyms. The full step-by-step breakdown is on this page.

Reserve position for material (9)

17A — Reserve position for material (9) — SUBSTANCE