Would that work for your situation?

A solution might be to allow an optional parameter 'regexp' inside the 
'parse' settings that would be used instead of the 'format' string to 
parse out the composition fields.

No, because that would take away flexibility in the parsing rules. And 
we are using the same strings for formatting and parsing composite 
strings. The formatting rules can be specified arbitrarily, whitespace 
splitting is not suffiecient. sscanf() is the only available 
counterpart method to printf formatting. And we probably don't want to 
implement sscanf() in PHP.

Summary: Surname or name of contact are possibly damaged when adding
contact to address book in case the data is UTF-8 encoded. A part of
multibyte character in surname or name is sometimes treated as a
whitespace when sscanf() is called.

Analysis: There is sscanf() function used in /turba/lib/Driver.php:

$splitval = sscanf($val, $parse['format']);

$var can be a multibyte string (UTF-8 encoded).

sscanf(), as a PHP String function, doesn't handle multibyte encodings 
such as UTF-8.

So, instead of sscanf(), another way of composite fields computing 
should be used.

Please note 1: PHP manual says: sscanf() function is not locale-aware. 
This is not true. PHP's sscanf() uses isspace() system function call 
which is locale-aware. Moreover, isspace() works as expected only for 
alphanumeric characters and symbols. The results of isspace() on other 
than these bytes of unsigned char type is unpredictable in general. 
Therefore composite name computing with sscanf() may or may not 
succeed, and eventually success is not the proof of code correctness.

Please note 2: this was reported with Ticket #10956 and shown to 
slusarz@horde.org who wasn't able to reproduce this issue. IMHO the 
ability to reproduce the issue depends on subtle operating system 
details (i.e. on isspace() implementation).

Please note 3: So, this could be in fact Solaris (not Horde) issue 
(doesn't happen under Ubuntu Linux for instance). Solaris isspace() is 
badly damaged. However you shouldn't use sscanf() there because data 
can be multibyte. But there is no similar multibyte function in PHP. I 
think PHP needs something like swscanf(). Maybe Multibyte String or 
intl functions could be used.

But in this case the problem is to find three substrings separated by 
space(s). explode() should be enough?