A Pascal program  is  composed  entirely  of  lexical  elements.
  These  elements  are  individual  symbols,  such  as  arithmetic
  operators, or they may be words that have  special  meanings  in
  Pascal.   The  basic unit of any lexical element is a character,
  which must be a member of the ASCII character set.

  The  words  used  in  a  Pascal  program  are  combinations   of
  alphabetic and numeric characters and occasionally a dollar sign
  ($), an underscore (_), or a percent sign (%).  Some  words  are
  reserved for the names of executable statements, operations, and
  predefined data structures.  Other words in a Pascal program are
  identifiers.   Predeclared  identifiers  represent  routines and
  data types  provided  by  VSI  Pascal.   Other  identifiers  are
  created  by  the  use  to  name  programs,  symbolic  constants,
  variables, and any necessary  program  elements  that  have  not
  already been named.