A character string which specifies a search pattern
A function taking one argument which will return either nil or non-nil.
A list of all symbols defined in the system which match the given pattern, and if the predicate is supplied, whose values are true under that predicate.
This function searches the names of all defined symbols in the currently running interpreter environment. The pattern can contain the following special characters:
* matches any number of characters, including zero.
[c] matches a single character which is a member of the set contained within the square brackets.
[^c] matches any single character which is not a member of the set contained within the square brackets.
? matches a single character.
{xx,yy} matches either of the simple strings contained within the braces.
\c (a backslash followed by a character) - matches that character.
The predicate is any function which accepts a single argument. If the predicate evaluates to non-nil when given the value of a symbol, and if the symbol matches the pattern, then the symbol will be reported by apropos. If the predicate is not supplied, then all symbols which match the pattern will be reported. The pattern is case-sensitive.
Gamma> apropos("s*", function_p);
(setq strchr string symbol)
Gamma> apropos("?[sli]{igc,er}*");
(SIGCHLD SIGCONT dlerror)