Grouping UT labeling / underscore in annotation class name

If an annotation feature class contains several annotation classes that cannot be uniquely assigned to a master feature due to their SQL query and several annotation classes have the same name, then these annotation classes are made uniquely assignable to the master feature by a name prefix.  Something like this may be necessary for line annotations, for example.

The names of the annotation classes must then be structured as follows:

<Grouping>_<Description>

where
<Grouping> (= subtype identifier of the master feature, e.g. the line) and
<Description> must each have unique notations within the annotation featureclass.

<Grouping> must not contain an underscore '_' itself

Example:

ATTENTION: A stumbling block may be lurking here:
Underscores in the name of an annotation class are only allowed for the purpose of grouping because of this mechanism. All other annotation class names must not contain underscores!