Very simple example XBL control for Orbeon Forms

country-selector.xbl

<xbl:xbl xmlns:xh="http://www.w3.org/1999/xhtml"
         xmlns:xf="http://www.w3.org/2002/xforms"
         xmlns:ev="http://www.w3.org/2001/xml-events"
         xmlns:xxf="http://orbeon.org/oxf/xml/xforms"
         xmlns:my="http://www.example.com/"
         xmlns:saxon="http://saxon.sf.net/"
         xmlns:fb="http://orbeon.org/oxf/xml/form-builder"
         xmlns:xbl="http://www.w3.org/ns/xbl"
         xmlns:xxbl="http://orbeon.org/oxf/xml/xbl">

    <metadata xmlns="http://orbeon.org/oxf/xml/form-builder">
        <display-name lang="en">Custom Controls</display-name>
    </metadata>

    <xbl:binding id="my-country-selector" element="my|country-selector" xxbl:mode="lhha binding value">
        <fb:metadata>
            <fb:display-name lang="en">Country Selector</fb:display-name>
            <fb:icon lang="en">
                <fb:small-icon>/forms/orbeon/builder/images/dropdown.png</fb:small-icon>
                <fb:large-icon>/forms/orbeon/builder/images/dropdown.png</fb:large-icon>
            </fb:icon>
            <fb:template>
                <my:country-selector>
                    <xf:label ref=""/>
                    <xf:hint ref=""/>
                    <xf:help ref=""/>
                    <xf:alert ref=""/>
                </my:country-selector>
            </fb:template>
        </fb:metadata>
        <xbl:template>
            <xf:select1 appearance="minimal" ref="xxf:binding('my-country-selector')">
                <xf:item>
                    <xf:label>[Select...]</xf:label>
                    <xf:value/>
                </xf:item>
                <xf:itemset nodeset="doc('oxf:/forms/orbeon/controls/service/countries.xml')/countries/country">
                    <xf:label ref="name"/>
                    <xf:value ref="us-code"/>
                </xf:itemset>
            </xf:select1>
        </xbl:template>
    </xbl:binding>
</xbl:xbl>