src/vs/workbench/contrib/comments/browser/commentsEditorContribution.ts/CommentController/onEditorMouseDown
class CommentController:	private onEditorMouseDown(e: IEditorMouseEvent): void {
		this.mouseDownInfo = null;

		const range = e.target.range;

		if (!range) {
			return;
		}

		if (!e.event.leftButton) {
			return;
		}

		if (e.target.type !== MouseTargetType.GUTTER_LINE_DECORATIONS) {
			return;
		}

		const data = e.target.detail as IMarginData;
		const gutterOffsetX = data.offsetX - data.glyphMarginWidth - data.lineNumbersWidth - data.glyphMarginLeft;

		// don't collide with folding and git decorations
		if (gutterOffsetX > 14) {
			return;
		}

		this.mouseDownInfo = { lineNumber: range.startLineNumber };
	}