code: @Override
      public String concat(final String parent, final String name) {
          return parent != null
                  ? FileNameUtil.concat(FileNameUtil.getPath(parent), name)
                  : name;
      }
docs: get child template name by parent template name and relative name.
  
  <pre>
  example:
  /path/to/tmpl1.wit , tmpl2.wit =&gt; /path/to/tmpl2.wit
  /path/to/tmpl1.wit , /tmpl2.wit =&gt; /tmpl2.wit
  /path/to/tmpl1.wit , ./tmpl2.wit =&gt; /path/to/tmpl2.wit
  /path/to/tmpl1.wit , ../tmpl2.wit =&gt; /path/tmpl2.wit
  </pre>
  
  @param parent parent template's name
  @param name   relative name
  @return child template's name