Method parseStringGroup

static/katex/katex.mjs:15424–15475

* Parses a group, essentially returning the string formed by the * brace-enclosed tokens plus some position information.

(modeName, // Used to describe the mode in error messages.
  optional, raw)

  parseStringGroup(modeName, // Used to describe the mode in error messages.
  optional, raw) {
    const groupBegin = optional ? "[" : "{";
    const groupEnd = optional ? "]" : "}";
    const nextToken = this.nextToken;

    if (nextToken.text !== groupBegin) {
      if (optional) {
        return null;
      } else if (raw && nextToken.text !== "EOF" && /[^{}[\]]/.test(nextToken.text)) {
        // allow a single character in raw string group
        this.gullet.lexer.setCatcode("%", 14); // reset the catcode of %

        this.consume();
        return nextToken;
      }
    }

    const outerMode = this.mode;
    this.mode = "text";
    this.expect(groupBegin);
    let str = "";
    const firstToken = this.nextToken;
    let nested = 0; // allow nested braces in raw string group

    let lastToken = firstToken;

    while (raw && nested > 0 || this.nextToken.text !== groupEnd) {
      switch (this.nextToken.text) {
        case "EOF":
          throw new ParseError("Unexpected end of input in " + modeName, firstToken.range(lastToken, str));

        case groupBegin:
          nested++;
          break;

        case groupEnd:
          nested--;
          break;
      }

      lastToken = this.nextToken;
      str += lastToken.text;
      this.consume();
    }

    this.mode = outerMode;
    this.gullet.lexer.setCatcode("%", 14); // reset the catcode of %

    this.expect(groupEnd);
    return firstToken.range(lastToken, str);
  }
  /**
   * Parses a regex-delimited group: the largest sequence of tokens
   * whose concatenated strings match `regex`. Returns the string