How Documents Know Their Parents

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.. That's the entire point: The creator code tel

5.6 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

So how does Mac OS X know how to find a document's mommy?

It actually has four different mechanisms

• Your preferences If you've used the "Always Open with" command to specify a program (Section 5.6.1.1), that's the one that opens

• Type/Creator codes First, it checks to see if the document has an invisible, four-letter Type code and Creator code It does that because that's how Mac OS 9 used

to recognize documents, and Mac OS X wants to ensure compatibility (Apple used to monitor and track these four-letter codes, in conjunction with the various Mac software companies, so that no two creator codes were alike.)

The Creator code is the same for a program and the documents it creates—MSWD for Microsoft Word, FMP7 for FileMaker Pro, and so on That's the entire point: The creator code tells the Mac which program to open when you double-click a particular document

The Type code, meanwhile, specifies the document's file format: GIF, JPEG, TIFF, and so on

UP TO SPEED Window Layering

Mac OS X takes a layered approach to your programs' windows They're not all

in front or all in back; it's entirely possible to wind up with the windows of

different programs sandwiched and layered, front to back

Suppose, for example, you have Microsoft Excel in the foreground, but Word in the back-ground If you click within a visible portion of a background window, you bring only that window of Word to the front

The remedy for this situation, if it bothers you, is the Window Bring All to Front command, which appears in the Finder and many other programs It

brings all of a program's windows to the front (You can do the same thing by

simply clicking the program's Dock icon, or using the -Tab "heads-up"

display.)

In the Finder, if you prefer, you can also use the Window Arrange in Front command To reveal it, press Option as you open the Window menu (What

used to say "Bring All to Front" changes to say "Arrange in Front.") Mac OS X responds by cascading all open Finder windows, stacking them diagonally,

overlapping them so that only their title bars are visible

Layered windows shine when you're comparing two documents in two different programs, because it frees you of the window clutter of other open documents But the time will come when you're ready to bring all of a background

program's windows to the front

Get into the habit of clicking its Dock icon, or pressing -Tab to select its

icon, rather than clicking inside one window When you do that, all open

windows in that application come forward, from wherever they may be

When you double-click a document, Mac OS X checks to see if it has a creator code If so, it then consults an invisible database of icons and codes, the master index that lists the correspondence between creator codes and the applications that generate them

If the desktop file discovers a match, then the corresponding program opens the document, which now appears on your screen

• Unix database If the document doesn't have Type or Creator codes (and

documents created by Cocoa programs—see Section 5.9—generally don't), Mac

OS X consults a second internal Mac OS X database, one that's inherited from Unix systems The only real interaction you have with it is when you change a document's parent to a different program, as described on the following pages (Actually, you can open and examine the database—if you're a programmer/geek.)

• Filename extensions A filename extension is a suffix following a period in the file's name, as in Letter to Mom.doc (It's usually three letters long, but doesn't have to be.) These, too, play a role in determining which documents open into which programs—as the operating system's last resort

Figure 5-11 Top: In the Info window, open the Name & Extension pane Now you can see what Mac OS X really thinks your file is called Turn "Hide extension" on if

you'd rather not see the file name suffix in the Finder

Bottom: If you try to add a suffix of your own, Mac OS X objects, in effect saying,

"Hey—I've already got a filename extension for this, even if you can't see it Are you sure you know what you're doing?" (And hallelujah—in Leopard, you can turn off this warning, if you like Choose Finder Preferences Advanced pane Turn

off "Show warning before changing an extension.")

That's how Windows identifies its documents 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

Note: Mac OS X comes set to hide most filename extensions, on the premise that they

make the operating system look more technical and threatening If you'd like to see them, however, choose Finder Preferences, click the Advanced button, and then turn on

"Show all file extensions." Now examine a few of your documents; you'll see that their names now display the previously hidden suffixes.You can hide or show these suffixes on

an icon-at-a-time basis, too (or a clump-at-a-time basis) Just highlight the icon or icons you want to affect, and then choose File Get Info In the resulting Info window,

proceed as shown in Figure 5-11

It's possible to live a long and happy life without knowing anything about these codes and suffixes Indeed, the vast majority of Mac fans may never even encounter them But if you're prepared for a little bit of technical bushwhacking, you may discover that

understanding creator/type codes and file name suffixes can be useful in troubleshooting, keeping your files private, and appreciating how Mac OS X works

GEM IN THE ROUGH Using the Dock or Sidebar for Drag-and-Drop

The Mac is smart about the relationship between documents and applications If you double-click a TextEdit document icon, for example, TextEdit opens

automatically and shows you the document

But it's occasionally useful to open a document using a program other than the

one that created it Perhaps, as is often the case with downloaded Internet

graphics, you don't have the program that created it, or you don't know which

one was used This technique is also useful when opening a Read Me file into

your word processor, such as Word, instead of the usual TextEdit program

In such cases, the Dock is handy: Just drag the mystery document onto one of

the Dock's tiles, as shown here Doing so forces the program to open the

document—if it can (Dragging onto a program's icon in the Sidebar or even the Finder toolbar works just as well.)

Incidentally, in general, only the Dock icons of programs that can, in fact, open the file you're dragging become highlighted The others just shrug indifferently

or even scoot aside, thinking you're trying to drag the file into the dock

Pressing Option- as you drag forces Dock icons to be more tolerant Now

all of them "light up" as your document touches them, indicating that they'll try

to open your file Even so, a "could not be opened" error message may result

As they say in Cupertino, sometimes what a can really needs is a can opener

5.6.1 Reassigning Documents to Programs

Unfortunately, Type and Creator codes aren't of much use when you encounter a

document created by a program that you don't have If someone emails you a MIDI file (a file-exchange format for music) that she exported from the Finale sheet-music program, you won't be able to open it by double-clicking, unless you, too, have Finale installed Even if you have a different sheet-music program on your hard drive, just double-clicking the MIDI file won't, by itself, open it

Filename extensions, meanwhile, have problems of their own Filename extensions are even less likely to pinpoint which parent program should open a particular document Suppose you've downloaded a graphic called Sunset.jpg Well, almost any program these days can open a JPEG graphic—Photoshop, Word, Preview, Safari, and so on How does Mac OS X know which of these programs to open when you double-click the file?

Fortunately, you can decide You can reassign a document (or all documents of its kind)

to a specific program Here's the rundown

5.6.1.1 Reassigning a certain document—just once

Double-clicking a graphics file generally opens it in Preview, the graphics viewer

included with Mac OS X (see Section 10.23) Most of the time, that's a perfectly good arrangement But Preview has only limited editing powers What if you decide to edit a graphics file more substantially? You'd want it to open, just this once, into a different program—Photoshop Elements, for example

To do so, you must access the Open With command You can find it in two places:

• Highlight the icon, and then choose File Open With

• Control-click (or right-click) the file's icon Or, in a Finder window, highlight the icon and then open the Action menu In the shortcut menu, choose Open With

Study the submenu for a moment (Figure 5-12, top) The program whose name says

"(default)" indicates which program usually opens this kind of document From this

pop-up menu, choose the name of the program you'd rather open this particular file, right now, just this once

5.6.1.2 Reassigning a certain document—permanently

After opening a TIFF file in, say, Photoshop Elements for editing, you haven't really made any changes in the fabric of your Mac universe The next time you double-click that file, it opens once again in Preview

If you wish this particular file would always open in Photoshop Elements, the steps are slightly different In fact, there are three different ways:

• In the Choose an Application dialog box, turn on "Always Open With"(shown at bottom in Figure 5-12)

Start out with one of the previously described techniques (File Open With, or Control-click/right-click the file's icon and choose Open With)—but after you see the menu, press the Option key, too Before your very eyes, the Open With

command changes to say Always Open With

Figure 5-12 Top: The shortcut menu offers a list of programs capable of opening an icon If you were to press the Option key right now, the words Open With would suddenly change to say Always Open With

Bottom: If you choose Other, you're prompted to choose a different program Turn on Always Open With if you'll always want this document to open in the

new parent program Otherwise, this is a one-time reassignment

• Highlight the icon, and then choose File Get Info Open the "Open with"

panel Choose a new "parent" program's name from the pop-up menu You'll see that the word "(default)" changes position, now tacking itself onto the name of the new program you've chosen

Tip: You can use a similar trick to reassign the parenthood of a whole flock of selected

icons at once Once you've selected them, keep the Option key pressed as you choose File Show Inspector In the "Open with" section of this specialized GetInfo window, choose an ew program from the pop-up menu The message at the top of the window—

"22 items," for example—reminds you that you're changing the whole batch at once

5.6.1.3 Reassigning all documents of one type

So much for reassigning one document (or group of documents) at a time What if you're writing, say, a book about Mac OS X, and you've been taking a lot of screenshots? Mac

OS X saves each captured screen illustration as a graphics file in something called PNG format That's all fine, except that every time you double-click one of these, it opens into Preview, where you can't paint out unwanted details

You could reassign all of these files, one at a time, to a different program, but your

grandchildren would have grandchildren by the time you finish In this case, you want to tell Mac OS X, "For heaven's sake, make all PNG files open in Photoshop from now on!"

To make it happen, start by highlighting any PNG file Choose File Get Info (The shortcut menus won't help you in this case.) Open the "Open with" panel

From its pop-up menu, choose the program you want to open this kind of document from now on (If the one you prefer isn't listed, use the Other option, which opens the Choose

an Application dialog box so that you can navigate to the one you want Find and double-click the program.)

This time, follow up by clicking Change All beneath the pop-up menu (This button is dimmed until you've actually selected a different program from the pop-up menu.) Mac

OS X asks you to confirm by clicking Continue or pressing Enter

From now on, double-clicking any similar kind of document opens it in the newly selected program