Hi guyz, 
    I was going through crm_lead_view.xml for Lead Form.  I couldn't understand how the domain is defined for this field "stage_id" in the Header tag.

<form string="Leads Form" version="7.0">
    <header>
        <button name="%(crm.action_crm_lead2opportunity_partner)d"
            string="Convert to Opportunity" type="action" states="draft,open,pending"
            help="Convert to Opportunity" class="oe_highlight" />
        <button name="case_reset" string="Reset" type="object" states="cancel" />
        <button name="case_cancel" string="Cancel Case" type="object"
            states="draft,open,pending" />
        <field name="stage_id" widget="statusbar" clickable="True"
            domain="['&amp;', '|', ('case_default', '=', True), ('section_ids', '=', section_id), '|', ('type', '=', type), ('type', '=', 'both')]"
            on_change="onchange_stage_id(stage_id)" />
    </header>

Can anyone explain how the domain is defined for field "stage_id" and what & means?