function getIddPrefix(country, callingCode, metadata) {
	const countryMetadata = new Metadata(metadata)
	countryMetadata.selectNumberingPlan(country, callingCode)
	if (countryMetadata.defaultIDDPrefix()) {
		return countryMetadata.defaultIDDPrefix()
	}
	if (SINGLE_IDD_PREFIX_REG_EXP.test(countryMetadata.IDDPrefix())) {
		return countryMetadata.IDDPrefix()
	}
}
Pattern that makes it easy to distinguish whether a region has a single
international dialing prefix or not. If a region has a single international
prefix (e.g. 011 in USA), it will be represented as a string that contains
a sequence of ASCII digits, and possibly a tilde, which signals waiting for
the tone. If there are multiple available international prefixes in a
region, they will be represented as a regex string that always contains one
or more characters that are not ASCII digits or a tilde.