Question: fail handling in ANT

[Jiong Wei]

I notice the "failonerror" attribute only available for the following tasks:
        <apply> <exec> <execon> <java>
        <javac> <javadoc> and .NET tasks

If true, then how to fail a build when such as a critical <copy> failed?
Currently, even when the src file is missing, ant still continues.

Also, the I really have no clue how to tigger the <fail> task, is there a
ant property indicates the status of last operation?

Jiong