Method tryParseQuote

packages/icu-messageformat-parser/parser.ts:453–505

* Starting with ICU 4.8, an ASCII apostrophe only starts quoted text if it immediately precedes * a character that requires quoting (that is, "only where needed"), and works the same in * nested messages as on the top level of the pattern. The new behavior is otherwise compatible.

(parentArgType: ArgType)

   * nested messages as on the top level of the pattern. The new behavior is otherwise compatible.
   */
  private tryParseQuote(parentArgType: ArgType): string | null {
    if (this.isEOF() || this.char() !== 39 /* `'` */) {
      return null
    }

    // Parse escaped char following the apostrophe, or early return if there is no escaped char.
    // Check if is valid escaped character
    switch (this.peek()) {
      case 39 /* `'` */:
        // double quote, should return as a single quote.
        this.bump()
        this.bump()
        return "'"
      // '{', '<', '>', '}'
      case 123:
      case 60:
      case 62:
      case 125:
        break
      case 35: // '#'
        if (parentArgType === 'plural' || parentArgType === 'selectordinal') {
          break
        }
        return null
      default:
        return null
    }

    this.bump() // apostrophe
    const codePoints = [this.char()] // escaped char
    this.bump()

    // read chars until the optional closing apostrophe is found
    while (!this.isEOF()) {
      const ch = this.char()
      if (ch === 39 /* `'` */) {
        if (this.peek() === 39 /* `'` */) {
          codePoints.push(39)
          // Bump one more time because we need to skip 2 characters.
          this.bump()
        } else {
          // Optional closing apostrophe.
          this.bump()
          break
        }
      } else {
        codePoints.push(ch)
      }
      this.bump()
    }

    return String.fromCodePoint(...codePoints)
  }

  private tryParseUnquoted(
    nestingLevel: number,