Example of using dynamic values in a block

sample-layout.php

<reference name="head">
    <data service-call="selectedProductDetails" />
    <action method="setTitle"><title>{{data.selectedProductDetails.metaTitle}}</title></action>
    <action method="setKeywords"><keyword>{{data.selectedProductDetails.metaKeyword}}</keyword></action>
    <action method="setDescription"><description>{{data.selectedProductDetails.metaDescription}}</description></action>
</reference>