XML Demystified

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Working with Whitespace Characters
XML Demystifi ed
Each character on your keyboard is assigned a unique number called an ASCII
number. You don’t need to know these numbers, but if you’re curious, look up
“ASCII table” in a search engine and you’ll see the ASCII numbers.
Some characters are nonprintable characters, such as a space inserted when you
press the spacebar or the tab when you press the TAB key. These are referred to as
whitespace characters. You’ll find a list of these characters numbered from zero to
33 on the ASCII table.
Whitespace characters are inserted into a document to give instructions to the
program that reads the document. You don’t see these on the screen, but a program,
such as a parser, can see them.
For example, a carriage return and linefeed whitespace characters are inserted
into a document when you press the ENTER key. This gives the program instructions
to move the cursor to the beginning of the next line.
You can tell the parser how to handle whitespace characters that appear in an
XML document by using the xs:whiteSpace tag in the XML schema. There are
three things that you can do when you encounter a whitespace character in an XML
document: preserve, replace, or collapse.
Preserve means that the parser does nothing special with the whitespace character.
It simply passes the whitespace characters along with the rest of the XML document.
Replace tells the parse to replace all whitespace characters with a space. Collapse
tells the parser to replace all whitespace characters with spaces (similar to replace),
then it collapses multiple occurrences of whitespaces to a single space. Furthermore,
leading and trailing whitespaces are deleted.
You specify preserve, replace, and collapse as the value of the value attribute of
the xs:whiteSpace tag. Here is an example of preserve:
Restricting the Length of a Field
A seemingly endless number of characters can be used as the content of an element.
However, other applications that use the data might restrict the number of characters
they can receive from the XML document.