src/vs/base/common/filters.ts/_matchesPrefix
function _matchesPrefix(ignoreCase: boolean, word: string, wordToMatchAgainst: string): IMatch[] | null {
	if (!wordToMatchAgainst || wordToMatchAgainst.length < word.length) {
		return null;
	}

	let matches: boolean;
	if (ignoreCase) {
		matches = strings.startsWithIgnoreCase(wordToMatchAgainst, word);
	} else {
		matches = wordToMatchAgainst.indexOf(word) === 0;
	}

	if (!matches) {
		return null;
	}

	return word.length > 0 ? [{ start: 0, end: word.length }] : [];
}