puzzled about mako filters

[king wang]

I want convert \n to <br/> by self-defined filter:

<%

def brescape(text):

    return text.replace("\n", "<br/>")

%>

but I was puzzled with the following statement:

${"abc\ndef" | h, brescap}

what i expect:

when the h filter applied, the output should be abc\ndef.  

and the output should be abc<br/>def when the second filter brescape applied.

unexpected output:

abc&lt;br/&gt;def

Is there some who can tell me what happened？