[VEX] VEX expressions

VEX type	Syntax
float	f@name
vector2 (2 floats)	u@name
vector (3 floats)	v@name
vector4 (4 floats)	p@name
int	i@name
matrix2 (2×2 floats)	2@name
matrix3 (3×3 floats)	3@name
matrix (4×4 floats)	4@name
string	s@name

VEX type	Attribute names
vector (3 floats)	@P, @accel, @Cd, @N, @scale, @force, @rest, @torque, @up, @uv, @v @center, @dPdx, @dPdy, @dPdz (see Volume Wrangle).
vector4 (4 floats)	@backtrack, @orient, @rot
int	@id, @nextid, @pstate @elemnum, @ptnum, @primnum, vtxnum, @numelem, @numpt, @numprim, numvtx (see indexing variables below). @group_* (see accessing group membership below). @ix, @iy, @iz, @resx, @resy, @resz (see Volume Wrangle).
string	@name, @instance