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Index: X

x-height: em and ex units
XML (Extensible Markup Language): 1.2.6. Preparing for the Future
display property and: 2.9.1. Why Does the display Property Exist?
selectors in: 2.1.2. Simple Selectors

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Since we've given the "tall" text aline-height of 18px , thedifference between font-size andline-height is 6 pixels. In this case, though, thehalf-leading of 3 pixels is added to the content area, not subtracted(since the line-height is more than thefont-size). This will result in an inline box 18pixels tall, and its top is aligned with the top of the line box.Thus Figure 8-56.

"upright"text, which is probably best described as "text that is notitalic or otherwise slanted." The vast majority of text in thisbook is upright, for instance.

Thatleaves only an explanation of the difference betweenitalic and oblique text. Forof the positioned element should be placed from the top of itscontaining block. In the case of top, positivevalues move the top edge of the positioned elementdownward, while negative values move itabove the top of its containing block.Similarly, left describes how far to the right (forpositive values) or left (for negative values) the outer left edge ofthe positioned element is from the left edge of its containing block.Another way to look at it is that positive values cause inwardoffsets, moving the edges toward the center of the containing block,it a border style:

SPAN {border: 1px dashed black;}
Figure 8-45

Figure 8-45. A single-line inline element

This is the simplest case of an inline element contained by ablock-level element, no different in its way than a paragraph withtwo words in it. The only differences are that in Figure 8-45, we have a few dozen words and that mostparagraphs don't contain an explicit inline element such asSPAN.

By not predefining any tags in the XML Recommendation, the W3C allowed developers full control over customizing their data as they see fit. This makes XML very attractive to encoding data that already exists in legacy databases (by using database metadata, and other schema information). This extensibility of XML makes it such a great fit when trying to get different systems to work with each other.

XML supports shareable structure (using DTDs)

Since the structure of the XML document can be specified in DTDs they provide a simple way to make it easier to exchange XML documents that conform to a DTD. For example, if two software systems need to exchange information, then if both of the systems conform to one DTD, the two systems can process information from each other. DTDs are not as powerful as some kind of schema architecture for XML, they don't support typing, subclassing, or instantiation mechanisms that a schema architecture must have.

DTDs are a simple way to make sure that 2 or more XML documents are of the same "type". Its a very limited approach to making "typed" XML documents shareable across systems. In the future some kind of schema system will be proposed by the W3C that should allow typing, instantiation and inheritance of information (in XML).

XML enables interoperability



[ <length> | <percentage> ]{1,4}


Percentage values refer to the width of the parent element.