Here is what you need to do to add project based code assist to a custom component added in JBoss Developer Studio:
Create a new xml file in <JBDS_home>studio/eclipse/plugins/org.jboss.tools.common.kb_***/schemas/tld/. For example call it JeniaFaces.xml. The file should be written according to <JBDS_home>/studio/eclipse/plugins/org.jboss.tools.common.kb/kb.jar/org/jboss/tools/common/kb/kb-schema_1.0.dtd
Here is how you set what is available for code assist:
Adds code assist for JSF pre-defined objects, such as value= "#{param}" :
<AttributeType ...>
<proposal type="jsfVariables"/>
</AttributeType>
Adds bundle resource (property file) code assist:
<AttributeType ...>
<proposal type="bundleProperty"/>
</AttributeType>
Adds managed bean property code assist:
<AttributeType ...>
<proposal type="beanProperty"/>
</AttributeType>
Adds managed bean property but with a specified type:
<AttributeType ...>
<proposal type="beanProperty">
<param name="type" value="java.lang.Boolean"/>
</proposal>
</AttributeType>
Adds managed bean method with a signature:
<AttributeType ...>
<proposal type="beanMethodBySignature">
<param name="paramType" value="javax.faces.context.FacesContext"/>
<param name="paramType" value="javax.faces.component.UIComponent"/>
<param name="paramType" value="java.lang.Object"/>
<param name="returnType" value="void"/>
</proposal>
</AttributeType>
Add information on your xml file in <JBDS_home>/studio/eclipse/plugins/org.jboss.common.kb_***/plugin.xml
<tld
jsf="true"
name="Jenia Faces"
schema-location="schemas/tld/myJSF.xml"
uri="http://www.jenia.org/jsf/dataTools"/>
Restart Eclipse. You should now have code assist for the component.