Question

I must configure CKEditor to add a class-attribute to every p-tag in the content. You can do something similar with config.format_p but it will only apply the class-attribute to text that is marked as "normal" which is not default.

Edit:
I’m using the current version 3.6.2. Here are the relevant parts of my config:

CKEDITOR.editorConfig = function( config )
{   
    config.removeFormatTags = 'b,div,big,code,del,dfn,em,font,i,ins,kbd,q,samp,small,span,strike,strong,sub,sup,tt,u,var,form,input,textarea';

    config.format_p =
    {
        element: 'p',
        attributes:
        {
            'class': 'tiny_p'
        }
    };
    config.skin = "office2003";
    config.entities_processNumerical = true;
}

The config.format_p option only takes effect when user chooses "normal" from format-menu and config.removeFormatTags only works when user manually clicks the clean-button. Both should work automatically like it does in TinyMCE.

Answer 1

You can add html processor filter

editor.dataProcessor.htmlFilter.addRules({
    elements :{
        p : function( element ){
            if ( element.className.indexOf("thiny_p") < 0){
                element.className += 'thiny_p';
            }
        }
    }
});

Also, if it is not required to be created as ckedito plugin maybe before you send content to server you can use jQuery to change content

$("iframe", "#cke_editor1").contents().find("p").addClass("tiny_p");

or, if textarea (source) is active

var editor= $("textarea", "#cke_editor1"); 
editor.val(editor.val().replace(/<p>/gi, "<p class='thiny_p'>"))

you should tweak a bit .replace(/<p>/gi, "<p class='thiny_p'>") regular expression to support other cases.

EDIT

Finally got time to download and setup editor on my box, here is working plugin

CKEDITOR.plugins.add( 'customparagraph',
{
    init: function( editor )
    {
        editor.addCommand('addParagraphClassName',{
            exec : function( editor ){    
                var ps = editor.document.$.getElementsByTagName("p");
                for (var i=0; i < ps.length; i++){

                    if(ps[i].className.indexOf("thiny_p") < 0){
                        ps[i].className += "thiny_p";
                    }

                }

            }
        });

        editor.ui.addButton( 'ThinyP',{
            label: 'Appends thiny_p class',
            command: 'addParagraphClassName',
            icon: this.path + 'images/icon.gif'
        });
    }
} );

put it in plugins/customparagraph/plugin.js
also create icon image plugins/customparagraph/images/icon.gif

in configuration you will have to add following configuration options config.js of you CKEdito installation

CKEDITOR.editorConfig = function( config )
{
    config.extraPlugins = "customparagraph";
    config.toolbar = [ [ 'ThinyP' ] ]; // add other toolbars and keep in mid this can be overwritten in page which loads CKEditor
};

OR

in page which loads CKEditor

<script type="text/javascript">
//<![CDATA[
    // Replace the <textarea id="editor1"> with a CKEditor
    // instance, using default configuration.
    CKEDITOR.replace( 'editor1',
        {
            extraPlugins : 'customparagraph',
            toolbar :
            [
                [ 'Bold', 'Italic', '-', 'NumberedList', 'BulletedList', '-', 'Link', 'Unlink' ],
                [ 'ThinyP' ]
            ]
        });
//]]>
</script>

User will have to click on toolbar button before save