NetBeans 5.5 Dev (Build 20060926 0000)
Java HotSpot(TM) Client VM 1.5.0_05-b05
Windows XP version 5.1 running on x86
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In response to issue 85838, I downloaded and installed the latest NB 5.5.

Code completion in NB 5.5 JSP editor does not recognise custom tag IDs.
e.g. the jsp:

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<%@ taglib uri="/WEB-INF/text-taglib.tld" prefix="tx"%>

<tx:text id="shlepcrab" scope="request">
How much crap could a crap crab grab
should a crab crab crept and grabbed
to shlep its crap
</tx:text>

<%= shlepcrab.[cursor]toString() %>
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Press [ctrl-space] at [cursor] and the response was "no suggestion".
In earlier versions of nb5 (or even nb6) I could get code completion pop-up 
menu. [f9] compiled the jsp without errors even though the editor did not 
recognise <%= shlepcrab.toString() %> .

*note~ tx:text is a simple jsp custom tag I wrote to allow multi-line blocks 
of text to be constructed without using the annoying string concat 
of "{string1}" + "{string2}" + ....