src/vs/workbench/api/common/extHostTypes.ts/SnippetTextEdit/isSnippetTextEdit
class SnippetTextEdit:	static isSnippetTextEdit(thing: any): thing is SnippetTextEdit {
		if (thing instanceof SnippetTextEdit) {
			return true;
		}
		if (!thing) {
			return false;
		}
		return Range.isRange((<SnippetTextEdit>thing).range)
			&& SnippetString.isSnippetString((<SnippetTextEdit>thing).snippet);
	}