Adds a component definition to the current project. A component definition is the same as a typedef except:
The purpose of this is to allow internal Apache Ant definitions to be made for tags like "and" or "or".
 <componentdef name="or" onerror="ignore"
    classname="com.apache.tools.ant.taskdefs.conditions.Or"/>
  <componentdef name="or" onerror="ignore"
    classname="com.apache.tools.ant.types.resources.selectors.Or"/>
  defines two components with the same name "or"; one is a condition (see conditions) and one is a selector (see selectors).