Edit Profile question

Hi There!

I'm working on creating an integration for JEvents RSVPro so EasySocial Fields can be used in a Registration form, everything works fine

I am now exploring the possibility of a user to be able to edit a particular field within the RSVPPro form. I am looking at default.edit.profile.php and each fields in the $step->fields array contains output key that contains the actual HTML output for the fields. I am wondering what triggers the output to be added to $step->fields field?

If this line of code from profile/view.html.php triggers it

                        // Trigger onEdit for custom fields.

			if( !empty( $step->fields ) )

			{

				$post = JRequest::get( 'post' );

				$args 	= array( &$post, &$my, $errors );

				$fields->trigger( 'onEdit' , SOCIAL_FIELDS_GROUP_USER , $step->fields , $args, $callback );

			}

which one does actually add output to the array?

A little help will be much appreciated

Thanks!