Mac OS X: The Missing Manual, Panther Edition

How Documents Know Their Parents

Every operating system needs a mechanism to associate documents with the applications that created them. When you double-click a Microsoft Word document icon, for example, it’s clear that you want Microsoft Word to launch and open the document.

In Windows, every document bears a three-letter file name suffix. If you double-click something called memo.doc, it opens in Microsoft Word. If you double-click memo. wri, it opens in Microsoft Write, and so on.

Mac OS 9 uses a similar system, except that you never see the identifying codes. Instead, it relies on invisible, four-letter creator codes and type codes. Apple carefully monitors and tracks these four-letter codes, in conjunction with the various Mac software companies, so that no two codes are alike.

NOSTALGIC CORNERWindow Layering

In Mac OS 9, bringing a program to the foreground also brought all of its windows to the foreground. If you were working in Internet Explorer, but Word was running in the background with six open documents, all six windows would pop to the front when you switched to Word.

As shown here, however, Mac OS X takes a much more layered approach. It’s entirely possible to wind up with the windows of different programs sandwiched and layered, front to back.

Suppose, for example, that you have Microsoft Excel in the foreground, but Word in the background. If you click within a visible portion of a background window, you bring only that window of Word to the front—a sandwiched effect ...