src/vs/editor/common/model/textModel.ts/TextModel/onBeforeAttached
class TextModel:	public onBeforeAttached(): void {
		this._attachedEditorCount++;
		if (this._attachedEditorCount === 1) {
			this._tokenizationTextModelPart.handleDidChangeAttached();
			this._onDidChangeAttached.fire(undefined);
		}
	}