Editing a garment
Two ways to say where a change goes, and one rule that governs both.
Parts
When a studio flat appears, the studio segments it and lights up what it found — neckline, sleeve, cuff, hem. That is a report, not a setting. It clears itself after a couple of seconds precisely so it does not quietly become one.
A part you select yourself does two things: it names the part in the instruction, and it scopes the edit to that part's pixels. The second is why a selection is not free.
A mask helps a change that stays inside the part, and forbids one that changes the part's outline.
Recolouring a cuff stays inside the cuff. A V-neck does not — the V has to cut below where the crew neck currently ends, and a mask cut to the crew neck masks away exactly the room it needs. So for necklines, collars, sleeve length and hem shape, the studio drops the mask and says so: “Not scoped to the neckline — this change needs room outside it.” Nothing is wrong when you see that.
Drawing an area
Select does the same job, with one difference: a drawn area is never second-guessed. Draw a bigger area to make room for a deeper neckline and that is taken as the instruction.
A masked edit that contradicts convention produces nothing at all.
Ask for a pocket mid-panel on a skirt and the image comes back unchanged. The model does not put it somewhere else — it declines. The same skirt that refuses mid-panel accepts a pocket at the hip every time. The studio detects this and tells you, rather than leaving you looking at an image that appears unchanged.
When you need something where the garment does not expect it, do not argue with the generator — place it.