Pattern rules:
  --------------
  case insensitive
  []     variable residues are surrounded by squared brakets
  .      a completely variable residue
  +      one or more residues, e.g. S+ for consecutive serines
  *      zero or more residues
  {a,b}  repeated between a and b times (or any if b non-specified)
  |      separate variants of a pattern
  ()     subsequences; above modifiers applies, e.g. (ATGC){3,3} will
         search ATCG repeated 3 times
  ^      restrict to the beginning of a sequence
  $      restrict to the end of a sequence
  
  Example: atg(...)+(tag|taa|tga) will find ORFs!
           [GC]{10,} for finding stretches of 10 or more G or C.