3. What
are MIME Types?
When
a web or WAP browser receives a document, it needs some way to
determine the type of contents the document contains so that it can
decide how to deal with the document.
MIME
(Multipurpose Internet Mail Extensions) is developed for such
purpose.
A
MIME type is associated to a file type.
For
example, the MIME type "text/html" is associated to HTML
files and the MIME type "text/vnd.wap.wml" is associated
to WML files.
Web
servers choose a suitable MIME type and include it in an HTTP response
automatically. They keep a conversion table that contains the
mappings between MIME types and file extensions.
For
example, let's say a WAP browser requests a WML file named
helloWorld.wml from a web / WAP server. The web / WAP server will search
for the MIME type associated to the ".wml" extension in the
conversion table and includes it in the HTTP response
automatically.
4. WAP 1.x / WAP 2.0
MIME Types and File Extensions
Before
a web / WAP server can be used to serve WAP 1.x or WAP 2.0 content,
you need to make sure its MIME settings have been configured
properly. Otherwise WAP browsers cannot display the WAP pages.
The
latest versions of some web servers have set the MIME types
of WAP 1.x and WAP 2.0 properly by default, which means you do not need to
modify anything.
The
following table lists the MIME types of WAP 1.x:
File
extension
|
MIME
type
|
Contents
of the file
|
.wml
|
text/vnd.wap.wml
|
WML
markup in plain-text form
|
.wmlc
|
application/vnd.wap.wmlc
|
Compiled
WML markup
|
.wbmp
|
image/vnd.wap.wbmp
|
WBMP
image
|
.wmls
|
text/vnd.wap.wmlscript
|
WMLScript
code in plain-text form
|
.wmlsc
|
application/vnd.wap.wmlscriptc
|
Compiled
WMLScript code
|
The
following table lists the MIME types of WAP 2.0:
File
extension
|
MIME
type
|
Contents
of the file
|
.xhtml
or .html or .htm
|
application/vnd.wap.xhtml+xml
or
application/xhtml+xml
or
text/html
|
XHTML
MP markup in plain-text form
|
.css
|
text/css
|
WCSS
(WAP CSS or Wireless CSS) code in plain-text form
|
As
you can see in the above table, there are three possible MIME types
for XHTML MP files:
application/vnd.wap.xhtml+xml This
is the MIME type specified by the Open Mobile Alliance. If
"application/vnd.wap.xhtml+xml" is not set as the MIME
type, XHTML MP documents cannot be viewed on some WAP browsers (e.g.
browsers on some Nokia Series 60 mobile phones).
application/xhtml+xml This
is the MIME type for XHTML Family document types. (XHTML MP belongs
to the XHTML family.)
text/html This
is the MIME type for HTML documents. XHTML MP is
HTML-compatible.
Advantage of using "text/html": Using "text/html"
ensures that XHTML MP documents can be displayed on ordinary web
browsers. Some web browsers (e.g. Internet Explorer 6) do not
display documents with MIME types like "application/vnd.wap.xhtml+xml" and "application/xhtml+xml". For
example, let's say "application/vnd.wap.xhtml+xml" is associated
to your XHTML MP documents. If you use IE 6 to load any one of them, it will
pop up a dialog box asking you whether to save the file on the hard disk.
Disadvantage of using "text/html": Browsers will
parse XHTML MP documents as HTML documents but not XML documents.
Hence, invalid XML syntax may not be detected.
Sometimes you may want to detect the MIME types supported
by a client browser and then assign an appropriate MIME type to your XHTML MP documents
dynamically. For example, if you find that a browser supports the
"application/vnd.wap.xhtml+xml" type, you will assign "application/vnd.wap.xhtml+xml" to
your XHTML MP documents. If you find that a browser only supports the "text/html"
type (e.g. IE 6), you will assign "text/html" to your XHTML MP documents. Please refer to the
"Choosing MIME Types Dynamically"
section of our XHTML MP tutorial if you want to learn the details.
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