A codegroup is a collection of functions or other code which can sensibly be grouped together. There's no particular semantics implied by the grouping, as far as this DTD is (currently) concerned.
However, the DTDs which include this programcode DTD may add
semantics to this element. For example, the DSSSL DTD maps this
element to the style-specification
element in the DSSSL architecture.
codegroup |_(docblock, |__routine+)
The programming language used by the code within the group. This will be set by the DTD which includes this programcode DTD, and you need not (indeed cannot) set it.