src/vs/editor/browser/viewParts/lineNumbers/lineNumbers.ts/LineNumbersOverlay/_getLineRenderLineNumber
class LineNumbersOverlay:	private _getLineRenderLineNumber(viewLineNumber: number): string {
		const modelPosition = this._context.viewModel.coordinatesConverter.convertViewPositionToModelPosition(new Position(viewLineNumber, 1));
		if (modelPosition.column !== 1) {
			return '';
		}
		const modelLineNumber = modelPosition.lineNumber;

		if (this._renderCustomLineNumbers) {
			return this._renderCustomLineNumbers(modelLineNumber);
		}

		if (this._renderLineNumbers === RenderLineNumbersType.Relative) {
			const diff = Math.abs(this._lastCursorModelPosition.lineNumber - modelLineNumber);
			if (diff === 0) {
				return '<span class="relative-current-line-number">' + modelLineNumber + '</span>';
			}
			return String(diff);
		}

		if (this._renderLineNumbers === RenderLineNumbersType.Interval) {
			if (this._lastCursorModelPosition.lineNumber === modelLineNumber) {
				return String(modelLineNumber);
			}
			if (modelLineNumber % 10 === 0) {
				return String(modelLineNumber);
			}
			return '';
		}

		return String(modelLineNumber);
	}