Use xsl:strip-space to get rid of whitespace-only nodes.

This top-level element with a single attribute, elements, is assigned a whitespace-separated list of element names that you want stripped of extra whitespace. Here, extra whitespace means whitespace-only text nodes. This means, for example, that the whitespace separating words in the previous comment element are significant because they are not whitespace only. On the other hand, the whitespace designated by the special symbols are whitespace only.

A common idiom uses <xsl:strip-space elements="*"/> to strip whitespace by default and xsl:preserve-space (see later) to override specific elements. In XSLT 2.0, you are also allowed to have elements="*:Name", which tells the processor to strip whitespace in all elements with the given local name regardless of namespace.

Use normalize-space to get rid of extra whitespace.

A common mistake is to assume that xsl:strip-space takes care of "extra" whitespace like that used to align text in the previous comment element. This is not the case. The parser always considers significant whitespace inside an element's text that is mixed with nonwhitespace. To remove this extra space, use normalize-space, as in <xsl:value-of select="normalize-space(comment)"/>.

Use translate to get rid of all whitespace.

Another common mistake is to assume normalize-space strips all whitespace. This is not the case. Instead, it strips only leading and trailing whitespace and converts multiple internal whitespace characters to single spaces. If you need to strip all whitespace, use TRanslate(something,'&#x20;&#xa;&#xd; &#x9;', '').

Use an empty xsl:text element to prevent terminating whitespace in the stylesheet from being considered relevant.

xsl:text is normally considered a way to preserve whitespace. However, a strategically placed empty xsl:text element can prevent trailing whitespace in the stylesheet from being interpreted as significant.

Use xsl:preserve-space to override xsl:strip-space for specific elements.

There is not much point in using xsl:preserve-space unless you also use xsl:strip-space. This is because the default behavior preserves space in the input document and documents loaded with the document( ) function.

Remember, MSXML strips whitespace-only text nodes by default. In this case, you can use xsl:preserve-space to counteract this nonconformance.

Use xsl:text to precisely specify text-output spacing.

All whitespace inside an xsl:text element is preserved. This preservation allows precise control over whitespace placement. Sometimes you can use xsl:text to simply introduce line breaks:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   
<xsl:output method="text"/>
<xsl:strip-space elements="*"/>
   
<xsl:template match="number">
  <xsl:value-of select="."/>
  <xsl:text>&#xa;</xsl:text>
</xsl:template>
</xsl:stylesheet>

However, the problem with outputting newline characters directly is that some platforms (e.g., Microsoft's) expect a line break to be represented as carriage- return plus newline. However, since XML parsers are required to convert carriage-return plus newline into a single newline, there is no way to create a platform-independent stylesheet. Fortunately, most Windows-based editors and the Windows command prompt handle single newlines correctly. The one exception is the notepad editor that comes free with Windows.

Use nonbreaking space characters.

XSLT does not treat the character #xA0; (nonbreaking space) as normal whitespace. In particular, xsl:strip-space and normalize-space( ) both ignore this character. If you need to strip whitespace most of the time but have specific instances when it should remain in place, you might try to use this character in the XML input. Nonbreaking space is particularly useful for HTML output, but may be of lesser value in other contexts (depending on how the renderer handles it).

A text node is never stripped unless it contains only whitespace characters (#x20, #x9, #xD, or #xA).

Although they are not all that common, you should also understand the effect of xml:space attributes in both the stylesheet and the input document(s).

If a text-node's ancestor element has an xml:space attribute with a value of preserve, and no closer ancestor element has xml:space with a value of default, then whitespace-only text nodes are not stripped.

The chapter now looks at the rules for stylesheets and source documents separately. For stylesheets, your options are simple.

The only stylesheet elements for which whitespace-only nodes are preserved by default are xsl:text. Here, "by default" means unless otherwise specified using xml:space="preserve" as stated earlier in Step 2. See Example 7-4 and Example 7-5.