[development] Block visibility

[Karthik]

Hi,

   I just noticed the introduction of the option to use PHP code to
control visibility (on the block configure page). Is there any
documentation on this or any links to the conversation that led to
this decision? Besides being IMHO decidedly un-user-friendly, this
could very likely lock an admin out of his entire site.

   I couldn't find any information on drupal.org or in the mailing
lists. Apologies if this has already been addressed elsewhere.

Thanks
Karthik.