control characters with no graphics plus, as an option, a set of additional
characters with graphics. The characters of the default character type must
include the Fortran character set and may include other characters.
The processor may support other character sets, one for each nondefault
character type. Each of these additional character sets is a subset of the
processor character set and must contain a character designated as a blank
The characters of the processor character set may be used in character context,
in comments, and in input/output records. (Recall that characters in a
character literal constant or in a character string edit descriptor are in character
context.) The processor may also represent and recognize lowercase letters.
However, each lowercase letter is considered the same as its corresponding
uppercase letter in all contexts except character context and input/output
3.7.2 Low-Level Syntax and Lexical Tokens
A Fortran statement is constructed from low-level syntax. The lexical tokens
are the basic language elements. They are described by low-level syntax rules
in terms of the characters of the Fortran character set. The lexical tokens consist
of names, keywords, literal constants, labels, delimiters, operators, and various
other basic symbols such as =, =>, :, ::, ;, and %.
3.7.3 Source Forms
Fortran has two source forms: ?xed source form and free source form.