add option to use a value's html field generation method

src/hdmf/container.py

@@ -626,7 +626,10 @@ def _generate_html_repr(self, fields, level=0, access_code="", is_field=False):
         if isinstance(fields, dict):
             for key, value in fields.items():
                 current_access_code = f"{access_code}.{key}" if is_field else f"{access_code}['{key}']"
-                html_repr += self._generate_field_html(key, value, level, current_access_code)
+                if hasattr(value, '_generate_field_html'):
+                    html_repr += value._generate_field_html(key, value, level, current_access_code)
+                else:
+                    html_repr += self._generate_field_html(key, value, level, current_access_code)
         elif isinstance(fields, list):
             for index, item in enumerate(fields):
                 access_code += f'[{index}]'