src/vs/editor/contrib/snippet/browser/snippetSession.ts/OneSnippet/activeChoice
class OneSnippet:	get activeChoice(): { choice: Choice; range: Range } | undefined {
		if (!this._placeholderDecorations) {
			return undefined;
		}
		const placeholder = this._placeholderGroups[this._placeholderGroupsIdx][0];
		if (!placeholder?.choice) {
			return undefined;
		}
		const id = this._placeholderDecorations.get(placeholder);
		if (!id) {
			return undefined;
		}
		const range = this._editor.getModel().getDecorationRange(id);
		if (!range) {
			return undefined;
		}
		return { range, choice: placeholder.choice };
	}