Just translated comments for the method of adding items to the context menu. List of menu items listed in the line 13. Taken from article http://community.modx-cms.ru/blog/research/9846.html

gistfile1.php

<?php

switch($modx->event->name){
    case 'OnManagerPageInit':
        
$JS = <<<JS
<script type="text/javascript">
Ext.onReady(function(){
    // Get a tree
    var tree = Ext.getCmp('modx-resource-tree');
    // Describes a rule the allowed child resources
    var resourcesRules = {
        modDocument: ['modStaticResource', 'modDocument']
    };
    // Write functions copying the values ​​of the object,
    // since we have a problem at the level of reference objects
    // ie changing one variable is changed and the other, if the object is common
    var copyObject = function(from){
        var to = {};
        for(i in from){
            to[i] = from[i];
        }
        return to;
    }    
    // We fix an initial set of classes
    var classes = copyObject(MODx.config.resource_classes);

    // Adding the function of changing a set of classes
    // when creating a context menu
    tree.on('loadCreateMenus', function(types){
        var node = this.getSelectionModel().getSelectedNode()
            ,classKey;

        if(resourcesRules && node && node.attributes 
                && (classKey = node.attributes.classKey)
                && resourcesRules[classKey]
        ){
            for(var i in types){
                if(!resourcesRules[classKey].in_array(i)){
                    delete  types[i];
                }
            }
        }    
        return true;
    }, tree);
    
    // Adding the recovery function set of classes
    // This function is executed after the formation of the menu because added later
    // than the basic method of the resource tree
    tree.on('contextmenu', function(){
        MODx.config.resource_classes = copyObject(classes);
    });
}); 
</script>
JS;
        $modx->regClientStartupScript($JS, true);
        break;
}

?>