Empty is a KeyFunc which always returns true and the empty string.

Env is a KeyFunc which always returns a string.

EnvPresent is a KeyFunc which returns an environment variable if it is present.

Expand expands a string and ignores any errors that occur - keys that are not recognized are replaced with the empty string.

ExpandStrict expands a string using a series of common format functions.

Identity is a KeyFunc that returns the same format rules.

Versions is a KeyFunc for retrieving information about the current version.

OverrideVersion is the latest version, exposed for testing.

ImageTemplate is a class to assist in expanding parameterized Docker image references from configuration or a file.

KeyFunc returns the value associated with the provided key or false if no such key exists.