CustomItemsBrowsePlugin.php

<?php

class CustomItemsBrowsePlugin extends Omeka_Plugin_AbstractPlugin
{
    protected $_hooks = array(
        'items_browse_sql'
    );

    public function hookItemsBrowseSql($args) {

        $select = $args['select'];
        $sort_string = "CASE WHEN et_sort.text REGEXP '<[^>]*>' = 1 THEN TRIM(SUBSTR(et_sort.text, INSTR(et_sort.text ,' '))) ELSE et_sort.text END ASC";
        $select->reset(Zend_Db_Select::ORDER);
        $sort_order = new Zend_Db_Expr($sort_string);
        $select->order($sort_order);
        get_db()->getTable('Item')->applySorting($select, 'Dublin Core,Title', 'ASC');

    }

}

@luku Thanks! For the correction, and for the suggestion on $sortDir. Yeah, as written this would fail on nested HTML, which is entirely possible to have. And agreed about the usefulness of a sort_key field.