RFC 3761:The E.164 to Uniform Resource Identifiers...
RFC-Ref

A - B - C - D - E - F - G - H - I - L - M - N - O - P - Q - R - S - T - U - V - W - Z

ALPHA

Click on the red underlined text to get to the source

2. The ENUM Application Specifications
... enumservice = type 0*(subtypespec) subtypespec = ":" subtype type = 1*32(ALPHA / DIGIT) subtype = 1*32(ALPHA ...
... ALPHA / DIGIT) subtype = 1*32(ALPHA / DIGIT) ...

A - B - C - D - E - F - G - H - I - L - M - N - O - P - Q - R - S - T - U - V - W - Z

Google
Web
RFC-Ref
RFC-Ref.org
Frontpage
Global Index
RFC
Sister Sites
Chess-Ref.org
Law-Ref.org
InChI.info
Zvon.org