By Slash Lane

Published: 09:30 AM EST

Mac OS X 10.5.2 Update, the next in a year-long series of planned updates to Apple's new Leopard operating system, promises to be one of the most hefty maintenance releases put out by the company for its operating system software in recent years.

According to people familiar with the matter, Tuesday evening gave way to the first test builds of the software update for developers, including a 354MB bare-bones delta build and a 362MB combo updater -- both of which were labeled Mac OS X 10.5.2 build 9C7.

The Cupertino-based Mac maker reportedly asked those developers to focus their testing efforts on an expansive list of components running some 37 items long. Among them were Data Detectors, the Mac OS X Dock, the Finder, grammar checking, iCal, iChat, Mail, Parental Controls, Quick Look, Rosetta, Safari, Time Machine, and Leopard's 802.11 AirPort implementation (which has troubled some MacBook users.)

Meanwhile, the list of fixes and Leopard code corrections already baked into the 10.5.2 release runs even larger at a whopping 76. In particular, Apple appears to have placed an extra emphasis on its implementation of CUPS (Common Unix Printing System), fixing several distinct issues with the modular printing system, such as problems with reverse order printing and print jobs that had been placed on hold. Fixes for AirPort shared printing were also implemented, according to those familiar with the software.

In addition, Apple continues to free its Rosetta PowerPC compatibility layer of memory leaks while also tying loose ends in the new version of its Mail client -- correcting anomalies with mail flags, the display of certain fonts in mail windows, and the way Mail data detectors interface with iCal.

Mac OS X 10.5.2 build 9C7 stands as just the first external distribution of the impending Leopard update, which is not expected for released to end users until early next year. Previous rumors had suggested the software could arrive alongside new hardware at next month's Macworld Expo, which kicks off January 15th.