[Exim] PCRE question in system filter

I'm having trouble with a regular expression match in my system filter
and I'm just not seeing what I'm doing wrong. I've been over the PCRE
doc several times and I think what I'm doing is correct but it still
doesn't match.

To match:

Subject: Something                     [abcde]

I'm using:

$h_subject matches "\\\\s{10,}\[\\\\w{4,8}\]"

an exim -d9 -bF shows:

Match expanded arguments:
  Subject = Something                     [abcde]
  Pattern = \s{10,}[\w{4,8}]
Sub-condition is false: $h_subject matches \\s{10,}[\\w{4,8}]

What am I missing here?

Thanks,

Tabor

-- 
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Tabor J. Wells                                     twells@???
Fsck It!                 Just another victim of the ambient morality