Editing Metafont (section)

===Syntax===
Metafont has numeric and string constant tokens with mainstream syntaxes; strings are delimited by <code>"</code> quotes, numeric constants can have decimals but not an [[scientific notation|exponent part]]. All other tokens are classified as ''symbolic'', and can be redefined arbitrarily; there is no restriction that tokens with certain meanings must have names consisting of certain characters. At runtime, there can additionally be ''capsule'' tokens, which are effectively constant value tokens of arbitrary type; in the source code those appear as symbolic tokens.

Except where characters are involved in numeric or string constants, the extent of the token containing a particular character depends on to which class the character belongs; unlike [[TeX]], Metafont has fixed character classes. The characters <code>,</code>, <code>;</code>, <code>(</code>, and <code>)</code> are "loners" and only form single character tokens. For the character classes <code><=>:|</code>, <code>‘’</code> (single quotes), <code>+-</code>, <code>/*\</code>, <code>!?</code>, <code>#&@$</code>, <code>^~</code>, <code>[</code>, <code>]</code>, <code>{}</code>, and <code>.</code>, as well as the class of underscore together with upper and lower case A–Z, the token consists of the longest consecutive sequence of characters from the same class. Whitespace characters don't contribute tokens. <code>%</code> starts a comment lasting until end of line.

A notable application of these rules is that <code>#</code> is frequently appearing as part of variable names in Metafont code, e.g. <code>em#</code> and <code>pt#</code>.

Delimiters (such as parentheses) do not have built-in meanings, instead there is a command that turns two symbolic tokens into a pair of matching delimiters, but normally Metafont programs use only the ordinary parentheses. Besides to override priorities in expressions, delimiters are also required around certain kinds of macro arguments.