code: public boolean isAbsolute() {
          int colonIndex = namespace.indexOf(':');
          if (colonIndex == -1) {
              return false;
          }
          for (int i = 0; i < colonIndex; i++) {
              char ch = namespace.charAt(i);
              if (!Character.isLetter(ch) && !Character.isDigit(ch) && ch != '.' && ch != '+' && ch != '-') {
                  return false;
              }
          }
          return true;
      }
docs: Determines if this IRI is absolute
  
  @return {@code true} if this IRI is absolute or {@code false} if this IRI
  is not absolute