Common Lisp the Language, 2nd Edition
The syntax of a logical pathname namestring is as follows:
logical-namestring ::= [host :] [;] {directory ;}*
[name] [. type [. version]
Note that a logical namestring has no device portion.
host ::= word
directory ::= word | wildcard-word | wildcard-inferiors
name ::= word | wildcard-word
type ::= word | wildcard-word
version ::= word | wildcard-word
word ::= {letter digit -}+
wildcard-word ::= [word] * {word *}* [word]
wildcard-inferiors ::= **
A word consists of one or more uppercase letters, digits, and hyphens.
A wildcard word consists of one or more asterisks, uppercase letters, digits, and hyphens, including at least one asterisk, with no two asterisks adjacent. Each asterisk matches a sequence of zero or more characters. The wildcard word * parses as :wild; all others parse as strings.
Lowercase letters may also appear in a word or wildcard word occurring in a namestring. Such letters are converted to uppercase when the namestring is converted to a pathname. The consequences of using other characters are unspecified.
The host is a word that has been defined as a logical pathname host by using setf with the function logical-pathname-translations.
There is no device, so the device component of a logical pathname is always :unspecific. No other component of a logical pathname can be :unspecific.
Each directory is a word, a wildcard word, or ** (which is parsed as :wild-inferiors). If a semicolon precedes the directories, the directory component is relative; otherwise it is absolute.
The name is a word or a wildcard word.
The type is a word or a wildcard word.
The version is a positive decimal integer or the word NEWEST (which is parsed as :newest) or * (which is parsed as :wild). The letters in NEWEST can be in either alphabetic case.
The consequences of using any value not specified here as a logical
pathname component are unspecified.
The null string "" is not a valid value for any component of a logical pathname,
since the null string is not a word or a wildcard word.
