\documentclass[]{article}
\usepackage{expkv-cs}
\ekvcSplit\foo
{
,height=2cm
,length=1cm
}
{%
height: #1\par
length: #2\par
}
\ekvcHash\Foo
{
,long height=2cm
,length=1cm
}
{%
height: \ekvcValue{height}{#1}\par
length: \ekvcValue{length}{#1}\par
}
\ekvcSecondaryKeys\foo
{
,alias width=length
,meta square={length={#1},height={#1}}
}
\ekvcSecondaryKeys\Foo
{
,alias width=length
,meta square={length={#1},height={#1}}
}
\usepackage{xparse}