I tried to use a component from a vector and pass it to a function in an 
isosurface, and the parser returned an error. Se minimal scene below. The 
parser seems to confuse the notations k.u (component of a vector) and x 
(variable for the isosurface). Is this a "feature" or a bug? Or have I 
misunderstood something?

***Minimal scene***
#declare Function = function(u, v) {u*v}
#declare k = <1, 1>;

isosurface {
	function {y-Function(k.v*x, k.u*z)}
}

***Output***
isosurface {

function {y-Function(k <----ERROR

Parse Error: Expected 'operand', uv vector identifier found instead

Returned from renderer with error status

***

The workaround I figured out was to declare the vector components to 
variables:
#declare ku = k.u;
#declare kv = k.v;

and then everything works fine:
isosurface {
	function {y-Function(kv*x, ku*z)}
}

-- 
light_source{20*y,1}#macro _(M,X,Y,P)#macro L(N,D)#if(N)#declare 
P=P+D;box{-
0.5,0.5translate z*mod(9*P.gray,4)pigment{rgb P}rotate 45*x+clock*y 
translate
P}L(N-1,D)#end#end#if(M)L(mod(M,8)<mod(X,3)mod(Y,3)1>-1)_(div(M,8)div(X,3)div
(Y,3)P)#end#end _(2301603551,12850,60365,20*z-5*x)plane{y,-9pigment{rgb 1}}

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