code: public SafeStyleBuilder fontFamilyAppend(String value, String... otherValues) {
      sanitizeAndAppendToFontFamily(value);
      for (String otherValue : otherValues) {
        sanitizeAndAppendToFontFamily(otherValue);
      }
      return this;
    }
docs: Appends {@code values} to the {@code font-family} property. Values will be comma separated.
  
  <p>If a value consists only of only ASCII alphabetic or '-' characters, it is appended as is,
  since it might be a generic font family (like {@code serif}) which must not be quoted. If a
  value contains other characters it will be quoted, since quoting might be required (for
  example, if the font name contains a space) and unnecessary quoting is allowed.
  
  <p>Values must contain only whitelisted characters; those are alphanumerics, space,
  tab, and the set {@code [+-.!#%_/*]}. In addition, comment markers - {@code //}, {@code /*},
  and <code>*&#47;</code>- are disallowed too. Non-conforming values are replaced with
  {@link #INNOCUOUS_PROPERTY_STRING}.
  
  @see "https://developer.mozilla.org/en-US/docs/Web/CSS/font-family"