":is" / ":contains" / ":matches"
There are three match types describing the matching : ":is", ":contains", and ":matches". Match type arguments are supplied to those commands which allow them to specify what kind of match is to be performed.
These are used as tagged arguments to tests that perform string comparison.
The ":contains" match type describes a substring match. If the value argument contains the key argument as a substring, the match is true. For instance, the string "frobnitzm" contains "frob" and "nit", but not "fbm". The null key ("") is contained in all values.
The ":is" match type describes an absolute match; if the contents of the first string are absolutely the same as the contents of the second string, they match. Only the string "frobnitzm" is the string "frobnitzm". The null key ":is" and only ":is" the null value.
The ":matches" version specifies a wildcard match using the characters "*" and "?". "*" matches zero or more characters, and "?" matches a single character. "?" and "*" may be escaped as "\\?" and "\\*" in strings to match against themselves. The first backslash escapes the second backslash; together, they escape the "*". This is awkward, but it is commonplace in several programming languages that use globs and regular expressions.
In order to specify what type of match is supposed to happen, commands that support matching take optional tagged arguments ":matches", ":is", and ":contains". Commands default to using ":is" matching if no match type argument is supplied. Note that these modifiers may interact with comparators; in particular, some comparators are not suitable for matching with ":contains" or ":matches". It is an error to use a comparator with ":contains" or ":matches" that is not compatible with it.
It is an error to give more than one of these arguments to a given command.
Core : Requires no import statement
RFC3028