Custom encoding name with spaces is not compiled

Summary

Originates from the forum: https://www.eclipse.org/forums/index.php/t/1108162/

It is requested to allow the space character in custom encoding names. At the moment, the custom encodings defined by the following regex are allowed: [A-Za-z][A-Za-z0-9_]*

The standard allows different characters as well, this is a limitation of the compiler.