请教关于<head></head>里的内容！

呵呵，keywords是页面关键字，供搜索引擎使用；
      refresh是自动页面刷新，可设置刷新时间和url；
      还有很多，stylesheet啦，设置cache啦，等等，查DW的帮助吧，不过其实常用的就这些啦。
7.4.4 Meta data
Note. The W3C Resource Description Framework (see [RDF10] [p.356] ) became a
W3C Recommendation in February 1999. RDF allows authors to specify
machine-readable metadata about HTML documents and other network-accessible
resources.
HTML lets authors specify meta data -- information about a document rather than
document content -- in a variety of ways.
For example, to specify the author of a document, one may use the META element
as follows:
<META name="Author" content="Dave Raggett">
The META element specifies a property (here "Author") and assigns a value to it
(here "Dave Raggett").
This specification does not define a set of legal meta data properties. The
meaning of a property and the set of legal values for that property should be defined
in a reference lexicon called a profile [p.68] . For example, a profile designed to help
search engines index documents might define properties such as "author",
"copyright", "keywords", etc.
Specifying meta data
In general, specifying meta data involves two steps:
1. Declaring a property and a value for that property. This may be done in two
ways:
1. From within a document, via the META element.
2. From outside a document, by linking to meta data via the LINK element
(see the section on link types [p.54] ).
2. Referring to a profile [p.68] where the property and its legal values are defined.
To designate a profile, use the profile attribute of the HEAD element.
Note that since a profile is defined for the HEAD element, the same profile applies
to all META and LINK elements in the document head.
User agents are not required to support meta data mechanisms. For those that
choose to support meta data, this specification does not define how meta data
should be interpreted.
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The META element
<!ELEMENT META - O EMPTY -- generic metainformation -->
<!ATTLIST META
%i18n; -- lang, dir, for use with content --
http-equiv NAME #IMPLIED -- HTTP response header name --
name NAME #IMPLIED -- metainformation name --
content CDATA #REQUIRED -- associated information --
scheme CDATA #IMPLIED -- select form of content --
>
Start tag: required, End tag: forbidden
Attribute definitions
For the following attributes, the permitted values and their interpretation are
profile dependent:
name = name [p.50] [CS] [p.49]
This attribute identifies a property name. This specification does not list legal
values for this attribute.
content = cdata [p.50] [CS] [p.49]
This attribute specifies a property’s value. This specification does not list legal
values for this attribute.
scheme = cdata [p.50] [CS] [p.49]
This attribute names a scheme to be used to interpret the property’s value (see
the section on profiles [p.68] for details).
http-equiv = name [p.50] [CI] [p.49]
This attribute may be used in place of the name attribute. HTTP servers use this
attribute to gather information for HTTP response message headers.
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
The META element can be used to identify properties of a document (e.g., author,
expiration date, a list of key words, etc.) and assign values to those properties. This
specification does not define a normative set of properties.
Each META element specifies a property/value pair. The name attribute identifies
the property and the content attribute specifies the property’s value.
For example, the following declaration sets a value for the Author property:
<META name="Author" content="Dave Raggett">
The lang attribute can be used with META to specify the language for the value of
the content attribute. This enables speech synthesizers to apply language
dependent pronunciation rules.
In this example, the author’s name is declared to be French:
24 Dec 1999 18:26 65
The global structure of an HTML document
<META name="Author" lang="fr" content="Arnaud Le Hors">
Note. The META element is a generic mechanism for specifying meta data.
However, some HTML elements and attributes already handle certain pieces of meta
data and may be used by authors instead of META to specify those pieces: the
TITLE element, the ADDRESS element, the INS and DEL elements, the title
attribute, and the cite attribute.
Note. When a property specified by a META element takes a value that is a URI
[p.51] , some authors prefer to specify the meta data via the LINK element. Thus,
the following meta data declaration:
<META name="DC.identifier"
content="http://www.ietf.org/rfc/rfc1866.txt">
might also be written:
<LINK rel="DC.identifier"
type="text/plain"
href="http://www.ietf.org/rfc/rfc1866.txt">
META and HTTP headers
The http-equiv attribute can be used in place of the name attribute and has a
special significance when documents are retrieved via the Hypertext Transfer
Protocol (HTTP). HTTP servers may use the property name specified by the
http-equiv attribute to create an [RFC822] [p.356] -style header in the HTTP
response. Please see the HTTP specification ([RFC2616] [p.354] ) for details on
valid HTTP headers.
The following sample META declaration:
<META http-equiv="Expires" content="Tue, 20 Aug 1996 14:25:27 GMT">
will result in the HTTP header:
Expires: Tue, 20 Aug 1996 14:25:27 GMT
This can be used by caches to determine when to fetch a fresh copy of the
associated document.
Note. Some user agents support the use of META to refresh the current page after
a specified number of seconds, with the option of replacing it by a different URI.
Authors should not use this technique to forward users to different pages, as this
makes the page inaccessible to some users. Instead, automatic page forwarding
should be done using server-side redirects.
META and search engines
A common use for META is to specify keywords that a search engine may use to
improve the quality of search results. When several META elements provide
language-dependent information about a document, search engines may filter on the
lang attribute to display search results using the language preferences of the user.
For example,
66 24 Dec 1999 18:26
The global structure of an HTML document
<-- For speakers of US English -->
<META name="keywords" lang="en-us"
content="vacation, Greece, sunshine">
<-- For speakers of British English -->
<META name="keywords" lang="en"
content="holiday, Greece, sunshine">
<-- For speakers of French -->
<META name="keywords" lang="fr"
content="vacances, Grèce, soleil">
The effectiveness of search engines can also be increased by using the LINK
element to specify links to translations of the document in other languages, links to
versions of the document in other media (e.g., PDF), and, when the document is part
of a collection, links to an appropriate starting point for browsing the collection.
Further help is provided in the section on helping search engines index your Web
site [p.339] .
META and PICS
The Platform for Internet Content Selection (PICS, specified in [PICS] [p.356] ) is an
infrastructure for associating labels (meta data) with Internet content. Originally
designed to help parents and teachers control what children can access on the
Internet, it also facilitates other uses for labels, including code signing, privacy, and
intellectual property rights management.
This example illustrates how one can use a META declaration to include a PICS
1.1 label:
<HEAD>
<META http-equiv="PICS-Label" content=’
(PICS-1.1 "http://www.gcf.org/v2.5"
labels on "1994.11.05T08:15-0500"
until "1995.12.31T23:59-0000"
for "http://w3.org/PICS/Overview.html"
ratings (suds 0.5 density 0 color/hue 1))
’>
<TITLE>... document title ...</TITLE>
</HEAD>
META and default information
The META element may be used to specify the default information for a document in
the following instances:
The default scripting language [p.253] .
The default style sheet language [p.186] .
The document character encoding [p.41] .
The following example specifies the character encoding [p.41] for a document as
being ISO-8859-5
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The global structure of an HTML document
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-5">
Meta data profiles
The profile attribute of the HEAD specifies the location of a meta data profile. The
value of the profile attribute is a URI. User agents may use this URI in two ways:
As a globally unique name. User agents may be able to recognize the name
(without actually retrieving the profile) and perform some activity based on
known conventions for that profile. For instance, search engines could provide
an interface for searching through catalogs of HTML documents, where these
documents all use the same profile for representing catalog entries.
As a link. User agents may dereference the URI and perform some activity
based on the actual definitions within the profile (e.g., authorize the usage of the
profile within the current HTML document). This specification does not define
formats for profiles.
This example refers to a hypothetical profile that defines useful properties for
document indexing. The properties defined by this profile -- including "author",
"copyright", "keywords", and "date" -- have their values set by subsequent META
declarations.
<HEAD profile="http://www.acme.com/profiles/core">
<TITLE>How to complete Memorandum cover sheets</TITLE>
<META name="author" content="John Doe">
<META name="copyright" content="© 1997 Acme Corp.">
<META name="keywords" content="corporate,guidelines,cataloging">
<META name="date" content="1994-11-06T08:49:37+00:00">
</HEAD>
As this specification is being written, it is common practice to use the date formats
described in [RFC2616] [p.354] , section 3.3. As these formats are relatively hard to
process, we recommend that authors use the [ISO8601] [p.353] date format. For
more information, see the sections on the INS and DEL elements.
The scheme attribute allows authors to provide user agents more context for the
correct interpretation of meta data. At times, such additional information may be
critical, as when meta data may be specified in different formats. For example, an
author might specify a date in the (ambiguous) format "10-9-97"; does this mean 9
October 1997 or 10 September 1997? The scheme attribute value
"Month-Day-Year" would disambiguate this date value.
At other times, the scheme attribute may provide helpful but non-critical
information to user agents.
For example, the following scheme declaration may help a user agent determine
that the value of the "identifier" property is an ISBN code number:
<META scheme="ISBN" name="identifier" content="0-8230-2355-9">
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The global structure of an HTML document
Values for the scheme attribute depend on the property name and the associated
profile.
Note. One sample profile is the Dublin Core (see [DCORE] [p.355] ). This profile
defines a set of recommended properties for electronic bibliographic descriptions,
and is intended to promote interoperability among disparate description models.
The global structure of an HTML document

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