Specifications for username

[Johann Spies <jspies@sun.ac.za>]

My manager wants to know what is allowed and what not when choosing a
linux username.

I know it must be lowercase, not have spaces or special characters,
but I don't know where it is documented.

Any reference to documentation that specify this?

Regards.
Johann
-- 
Johann Spies          Telefoon: 021-808 4036
Informasietegnologie, Universiteit van Stellenbosch

     "If we confess our sins, he is faithful and just to 
      forgive us our sins, and to cleanse us from all  
      unrighteousness."       I John 1:9