Reading through the l3draw documentation various matters came to mind:

Section 1.9 of l3draw.pdf
Typos
Text: \draw_transform_matrix:nnnnn
       has a fifth "n"
Margin: \draw_transform_xscale:n
       the second occurrence should be \draw_transform_yscale:n and not 
greyed out.
Text: \draw_transform_shift:n
       \draw_transform_xshift:n
      delete \draw_transform_shift:n
Margin: \draw_transform_matrix_reset
       needs a concluding colon

Clarification
Perhaps there should be a mention under 
\draw_transform_matrix_concat:nnnn that concatenating means matrix 
multiplication from the left.

Naming
There is \draw_transform_matrix_concat:nnnn and 
\draw_transform_shift_concat:n. The rotate, scale, shift and slant 
transforms are also concatenations but not so named (lack the _concat). 
I wonder if a better naming scheme might be to drop the _concat from 
\draw_transform_matrix_concat:nnnn and \draw_transform_shift_concat:n, 
thus treating all the concatenating transforms similarly, and rename the 
functions currently called \draw_transform_matrix:nnnn and 
\draw_transform_shift:n to something else, perhaps 
\draw_transform_matrix_set:nnnn and \draw_transform_shift_set:n?

Comma lists?
Was consideration given to using a comma list instead of four separate 
braced arguments for \draw_transform_matrix:nnnn? {a}{b}{c}{d} needs 
four brace pairs, {a,b,c,d} needs only one. I have a standard US 
keyboard (at least I think it is). The { and } characters require the 
shift key and a (small) stretch of the little finger to type; commas on 
the other hand are easy, no stretch, no shift key. Comma lists are 
widely used elsewhere in l3draw for specifying coordinate pairs, e.g. 
\draw_path_moveto:n { 1cm , 0cm }. Even {a,b}{c,d} would be better -- 
and helpful in separating the rows of the matrix.

Andrew


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