static setSpanValue(a, b, c) {
    if (a instanceof Span) {
      return a;
    } else {
      if (b === undefined) {
        return new Span(a);
      } else {
        if (c === undefined) return new Span(a, b);
        else return new Span(a, b, c);
      }
    }
  }
Returns a new Span object.
@param {*|Span} a - The first value or a Span object.
@param {*} [b] - The second value.
@param {*} [c] - The third value.
@returns {Span} A new Span instance.