code: function checkInclude5(i) {
    const start = i;
    let l;
  
    if (tokens[i].type === TokenType.PlusSign) i++;
    else return 0;
  
    if (l = checkIdentOrInterpolation(i)) i += l;
    else return 0;
  
    if (l = checkSC(i)) i += l;
  
    if (l = checkArguments(i)) i += l;
    else return 0;
  
    if (l = checkSC(i)) i += l;
  
    if (l = checkBlock(i)) i += l;
    else return 0;
  
    return i - start;
  }
docs: Check if token is part of an included mixin like `+nani(foo) {...}`
  @param {number} i Token's index number
  @return {number} Length of the include