Help templates using form values

[iabw]

I've been using help templates that require other fields' values. These templates are evaluated using form.getValue() when the user hovers over an input ( as my help fields are styled as tooltips ). For an average form, it would probably perform well enough to evaluate on all 'change' events ( and the option should be turned off by default anyway ).

Is this a feature that could be a useful option in the core library (ie, should I write it into Form / Field class and file a pull request), or is it better suited to a plugin?

It seems like the most basic implementation wouldn't be much more than inserting these 2 code blocks into

Form https://github.com/powmedia/backbone-forms/blob/master/src/form.js#L79

if ( options.helpTemplates ){
  this.listenTo( this, "change", function(){
    var formValues = this.getValues();
    _.each( fields, function(field){
      field.evaluateHelpTemplate( formValues );
    });
  });
}

Field

evaluateHelpTemplate: function( formValues ){
  //helpClassName should be a setting with a default, same as errorClassName
  this.$( this.helpClassName ).replaceWith( _.template( this.help, formValues ) );
}

[glenpike]

Probably better to mixin this functionality - I think we did some mixing in with functionality at work, but need to check before putting example in.