-When this constant is true, you can use the C<fetch,store,exists,delete> callbacks on hashes.
-Initial VMG_UVAR capability was introduced in perl 5.9.5, with a fully functional implementation
-shipped with perl 5.10.0.
+When this constant is true, you can use the I<fetch>, I<store>, I<exists> and I<delete> magics on hashes.
+Initial L</VMG_UVAR> capability was introduced in perl 5.9.5, with a fully functional implementation shipped with perl 5.10.0.
+
+=head2 C<VMG_COMPAT_SCALAR_LENGTH_NOLEN>
+
+True for perls that don't call I<len> magic when taking the C<length> of a magical scalar.
+
+=head2 C<VMG_COMPAT_SCALAR_NOLEN>
+
+True for perls that don't call I<len> magic on scalars.
+Implies L</VMG_COMPAT_SCALAR_LENGTH_NOLEN>.