# Functions
As finds the first error in err's tree that matches target, and if one is found, sets target to that error value and returns true.
Is reports whether any error in err's tree matches target.
Join returns an error that wraps the given errors.
New returns an error that formats as the given text.
Unwrap returns the result of calling the Unwrap method on err, if err's type contains an Unwrap method returning error.
# Variables
ErrUnsupported indicates that a requested operation cannot be performed, because it is unsupported.