vrkansagara / magentotinymceconfig

Module allowing you to add additional configuration elements to Magento's TinyMCE implementation.

Magento TinyMCE Config

This module makes adding additional settings to the TinyMCE init call simple.

After installing the module, copy the following file

js/pulsestorm_tinymceconfig.dist.js

to

js/pulsestorm_tinymceconfig.js

Add your additional settings at the following location in the above file

var settings = this.originalGetSettings(mode);
//add any extra settings you'd like below

//makes "placeholder" a valid element for inputs
settings.extended_valid_elements = 'input[placeholder|accept|alt|checked|disabled|maxlength|name|readonly|size|src|type|value]';
return settings;

Original Article: http://alanstorm.com/magento_html5_tinymce