Optical Margin Alignment
Ever since Gutenberg set out to print his Bible, typesetters have looked for ways to "balance" the edges of columns of text—particularly lines ending or beginning with punctuation. Because the eye doesn't "see" punctuation, it can sometimes appear that the left or right edges of some columns of type (especially justified type) are misaligned. Some other programs compensate for this problem by using a "hanging punctuation" feature, which pushes certain punctuation characters outside the text column. But there's more to making the edges of a column look even than just punctuation. Some characters can create a "ragged" look all by themselves—think of a "W," at the beginning of a line, for example.
When you select an InDesign story (with either the Selection or the Type tool) and turn on the Optical Margin Alignment option in the Story panel (choose Story from the Type menu to display the Story panel), the program balances the edges of the columns based on the appearance of all of the characters at the beginning or end of the lines in the column. This adjustment makes the columns appear more even—even though it sometimes means that characters are extending beyond the edges of the column (see Figure 4-71).
Figure 4-71 Optical Margin Alignment
The amount that InDesign "hangs" a character outside the text column depends on the setting you enter in the Base Size field of the Story panel (that's the field with the icon that looks like it would make a drop cap). In general, you should enter the point size of your body text in this field.
Unfortunately, it turns out that many designers don't like the look of Optical Margin Alignment. It's not that the feature is flawed; it's that designers (especially younger folks) have become so accustomed to their type lining up with a particular guide or ruler that they think it's wrong to have type inside or outside that (non-printing) line. Nevertheless, we encourage you to try turning it on and seeing how your readers like it—we think they'll find the text easier to read.
Ignore Optical Margin. Even if you do like Optical Margin Alignment, there's a good chance that you'll occasionally find a paragraph or two that you wish it wouldn't apply to. For example, monospaced code listings should not be optically aligned—that defeats the purpose of using a monospaced font. Fortunately, you have the option to turn off Optical Margin Alignment on a paragraph by paragraph basis or in a paragraph style.
To turn it off for one or more selected paragraphs, choose Ignore Optical Margin from the Control panel or Paragraph panel menu. To disable it in a paragraph style, turn on the Ignore Optical Margin checkbox in the Indents and Spacing pane of the Paragraph Style Options dialog box.