UML241 — No Rules for Element Names

UML specification does not provide exact rules for element names. For example, namespace "provides a means for resolving composite names, such as name1::name2::name3." What are the rules for the name1/2/3? Could we use spaces, dashes, digits?
For the class name we should: "capitalize the first letter of class names (if the character set supports uppercase)." But what are the rules for the class name? "A use case is shown as an ellipse, either containing the name of the use case or with the name of the use case placed below the ellipse." But what are the rules for the use case name?

There are no rules for names in UML. The UML standard does not restricted what characters can be used in a name
or how the name is constructed.
Disposition: Closed - No Change