I strongly believe that PHP needs to continue evolving and 
improving. However, I also recognise the importance of 
maintaining backwards compatibility.

To help balance these two conflicting desires, I have been 
kicking around the idea of implementing a set of tests to 
help determine when the behavior of a function changes.

The basic idea is to run the tests against the various 
version of PHP, compare the output and flag when 
differences crop up. Users would be able to run these 
tests using a make target. The data from these tests could 
be used by a utility program that walks a directory 
structure, reading php files and looking for 
functions/features that have changed behavior.

I would like to call these 'Lemosian Conformity Tests' in 
honor of Manuel's consistent and vociferous work on 
preserving BC. :) While I don't like his approach, I agree 
that it is a valid concern. Personally, rather than being 
chained to BC, I would rather that we actively work to 
help users deal with changes more effectively.

Additionally, these changes would help developers and the 
QA team spot unintentional changes to function behavior.