CLS (a subset of the CTS) details the minimum set of features and types a
given compiler must support
if these compiler is targeting the CLR. So this given features are garanteed
to be supported by all languages
that target the CLR.

If you're designing types that should be used between languages you
shouldn't take advantage of features
outside the CLS because members of this types might not be accessible by
programmers using other CLR
programming languages

RM