The regular expression:

(?-imsx:^(?:[*]|[a-zA-Z]|\d+\.))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    [*]                      any character of: '*'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    [a-zA-Z]                 any character of: 'a' to 'z', 'A' to 'Z'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
    \.                       '.'
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------