src/vs/editor/common/core/stringBuilder.ts/StringBuilder/appendCharCode
class StringBuilder:	public appendCharCode(charCode: number): void {
		const remainingSpace = this._capacity - this._bufferLength;

		if (remainingSpace <= 1) {
			if (remainingSpace === 0 || strings.isHighSurrogate(charCode)) {
				this._flushBuffer();
			}
		}

		this._buffer[this._bufferLength++] = charCode;
	}