ebxml-bp message

Subject: BTA-PreCondition/PostCondition in ebxmlbp-2.0.4-Example-os-PIP7C7For2.04-en.xml

From: "Moberg Dale" <dmoberg@axway.com>
To: <ebxml-bp@lists.oasis-open.org>,<ebxml-bp-comment@lists.oasis-open.org>
Date: Fri, 1 Aug 2008 13:16:29 -0700

BTA-PreCondition/PostCondition in ebxmlbp-2.0.4-Example-os-PIP7C7For2.04-en.xml

This is the only example I could find for BTA-Pre/PostCondition:
<PreCondition expression="true" expressionLanguage="DocumentEnvelope" />
<PostCondition expression="true" expressionLanguage="DocumentEnvelope" />

What's the meaning of this Pre/PostCondition?
Where is it defined?

Follow-Ups:
- RE: [ebxml-bp] BTA-PreCondition/PostCondition in ebxmlbp-2.0.4-Example-os-PIP7C7For2.04-en.xml
  - From: "Moberg Dale" <dmoberg@axway.com>