The "C" stands for "implemented in C". The C implemented methods (and other predefined methods of XOTcl) are documented in the language reference (
http://media.wu.ac.at/doc/langRef-xotcl.html). To see the source-code, you would have to study the implementation of XOTcl.
Concerning the dashes ('-'): One can invoke every defined method during object creation by prefixing the method name with the dash...