extensions/emmet/src/bufferStream.ts/DocumentStreamReader/next
class DocumentStreamReader:	next(): number {
		if (this.eof()) {
			return NaN;
		}

		const code = this.document.getText().charCodeAt(this.pos);
		this.pos++;

		if (this.eof()) {
			// restrict pos to eof, if in case it got moved beyond eof
			this.pos = this._eof;
		}

		return code;
	}