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HTML Filter

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Note

Indexing Service is no longer supported as of Windows XP and is unavailable for use as of Windows 8. Instead, use Windows Search for client side search and Microsoft Search Server Express for server side search.

 

The HTML implementation for the IFilter interface (in nlhtml.dll) extracts text and property information from the class "htmlfiles" so that it can be indexed by Indexing Service. Indexing Service calls the methods on this IFilter interface implementation when indexing HTML files. For a description of the association between filter and file type, see Finding the Filter DLL for a File.

You can use the <META> tag feature of HTML documents to convey special handling requests to the HTML filter. <META> tags occur near the beginning of an html file within the <HEAD> ... </HEAD> tags, as shown in the following example.

<head>
<META NAME="DESCRIPTION" CONTENT="This text will appear on the results page as the document's summary.">
</head>

Some HTML META tags are automatically mapped to well-known property set and property ID values so that queries on these properties will search the mapped contents. Examples include the following.

Property example Mapped to
<meta name="author" content="ruth"> The author property in the Summary Information property set.
<meta name="subject" content="word processing"> The subject property in the Summary Information property set.
<meta name="keywords" content="fonts, serif"> The keyword property in the Summary Information property set.
<meta name="ms.category" content="fiction"> The category property in the document Summary Information property set.

 

Here are some other special features of the HTML filter:

  • Creating special abstracts from files

    The filtering process can generate abstracts for each filtered file, which default to being a set of characters at the beginning of the file. As shown in the example at the beginning of this section, you can use the <META NAME="DESCRIPTION" ..> tag to instruct the filter to use the string following the CONTENT keyword as the document abstract.

  • Preventing individual files from being filtered

    Add the following meta tag to the file:

    <meta name="robots" content="noindex">

  • Setting the language code for a file to ensure the system chooses the correct language word breakers and noise word files

    Add the following meta tag to the file, where the content field specifies the appropriate language code (in characters or using the locale value):

    <meta name="ms.locale" content="EN"> or

    <meta name="ms.locale" content=1033>

You can also define new new property names to filter. For additional information, see Defining New Property Names for a Web Catalog.