HTML- CSS - Syntax of Conditional Comments(조건부)
Posted 06 26, 2009 12:51, Filed under: Language/WebStandards<!-- IE 가 아닐경우 -->
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참고 URL
http://msdn.microsoft.com/en-us/library/ms537512(VS.85).aspx
Syntax of Conditional Comments
The basic syntax of each type of comment is shown in the following table. The first comment shown is the basic HTML Comment, which is included for the purpose of comparison and to illustrate the different syntax used by each type of conditional comment.
| Comment type | Syntax or possible value |
|---|---|
| standard HTML comment | <!-- Comment content --> |
| downlevel-hidden | <!--[if expression]> HTML <![endif]--> |
| downlevel-revealed | <![if expression]> HTML <![endif]> |
The HTML shown inside the syntax block in each of the conditional comments denotes any block of HTML content, including script. Both types of conditional comment use a conditional expression to indicate whether the content inside the comment block should be parsed or ignored.
The conditional expression is formed from a combination of feature, operator, and/or value, as shown in the following table.
| Item | Example | Comment |
|---|---|---|
| IE | [if IE] | The only currently supported feature is the string "IE", corresponding to Internet Explorer. |
| value | [if IE 7] | An integer or floating point numeral corresponding to the version of the browser. Returns a Boolean value of true if the version number matches the browser version. For more information, see Version Vectors. |
| ! | [if !IE] | The NOT operator. This is placed immediately in front of the feature, operator, or subexpression to reverse the Boolean meaning of the expression. |
| lt | [if lt IE 5.5] | The less-than operator. Returns true if the first argument is less than the second argument. |
| lte | [if lte IE 6] | The less-than or equal operator. Returns true if the first argument is less than or equal to the second argument. |
| gt | [if gt IE 5] | The greater-than operator. Returns true if the first argument is greater than the second argument. |
| gte | [if gte IE 7] | The greater-than or equal operator. Returns true if the first argument is greater than or equal to the second argument. |
| ( ) | [if !(IE 7)] | Subexpression operators. Used in conjunction with boolean operators to create more complex expressions. |
| & | [if (gt IE 5)&(lt IE 7)] | The AND operator. Returns true if all subexpressions evaluate to true |
| | | [if (IE 6)|(IE 7)] | The OR operator. Returns true if any of the subexpressions evaluates to true. |
| true | [if true] | Always evaluates to true. |
| false | [if false] | Always evaluates to false. |
Downlevel-hidden Conditional Comments
The following sample shows a downlevel-hidden conditional comment, which contains a short paragraph of text.
<!--[if IE 5]>
<p>Welcome to Internet Explorer 5.</p>
<![endif]-->
The downlevel-hidden conditional comment contains hyphens ("--") in the opening and closing tag, similar to the basic HTML Comment. The condition appears in the opening portion of the tag, and [endif] is placed prior to the closing portion of the tag. The content is placed inside the comment tags.
Because the first four characters and the last three characters of the comment are identical to a basic HTML Comment element, downlevel browsers ignore the HTML content inside the comment block. Since content is effectively hidden from browsers that do not support conditional comments, this type of conditional comment is called downlevel-hidden.
If the result of the conditional expression is true, the content inside the comment block is parsed and rendered by Internet Explorer 5 and later versions. This behavior makes the downlevel-hidden conditional comment particularly useful for content that has been specifically designed for Internet Explorer.
The following sample illustrates how a client-side script block can be placed inside a conditional comment; in this case, a message is displayed in Internet Explorer 5 and later.
<!--[if gte IE 5]>
<SCRIPT LANGUAGE="Javascript">
alert("Congratulations! You are running Internet Explorer 5 or greater.");
</SCRIPT>
<P>Thank you for closing the message box.</P>
<![endif]-->
In the preceding example, only the major digit of the browser version is compared because it is the only digit specified in the conditional expression. To compare both major and minor version numbers, specify both digits. For further explanation and examples on specifying the browser's version number, see Version Vectors.
Downlevel-revealed Conditional Comments
The downlevel-revealed conditional comment enables you to include content in browsers that do not recognize conditional comments. Although the conditional comment itself is ignored, the HTML content inside it is not. Internet Explorer 5 and later versions also parse and render the content if the conditional expression evaluates to true. The downlevel-revealed conditional comment complements the downlevel-hidden conditional comment.
The following snippet shows a typical downlevel-revealed conditional comment.
<![if lt IE 5]>
<p>Please upgrade to Internet Explorer version 5.</p>
<![endif]>
When comparing this type of comment to the basic HTML Comment, notice that there are no hyphens ("--") immediately after the opening "<!" or immediately before the closing ">" of the comment block; therefore, the comment delimiters are treated as unrecognized HTML. Because the browser does not recognize the downlevel-revealed conditional comment, it does nothing with it.
Version Vectors
Conditional expressions are often used to determine the version of the browser. The format of the version vector number must be defined correctly to obtain the desired result.
When testing the major browser version number, the version vector is an integer. To check for a minor browser version, follow the version vector by a decimal point and four digits. For example, the version vector for the release build of Internet Explorer 5.5 is 5.5000.
In the following example, only the major version number is specified; therefore, the sample evaluates as true for both Internet Explorer 5 and Internet Explorer 5.5.
<!--[if IE 5]>
<p>Welcome to any incremental version of Internet Explorer 5!</p>
<![endif]-->
The following test correctly identifies Internet Explorer 5.
<!--[if IE 5.0000]>
<p>Welcome to Internet Explorer 5.0!</p>
<![endif]-->
Examples
Here are some more examples of conditional comments.<!--[if IE]><p>You are using Internet Explorer.</p><![endif]-->
<![if !IE]><p>You are not using Internet Explorer.</p><![endif]>
<!--[if IE 7]><p>Welcome to Internet Explorer 7!</p><![endif]-->
<!--[if !(IE 7)]><p>You are not using version 7.</p><![endif]-->
<!--[if gte IE 7]><p>You are using IE 7 or greater.</p><![endif]-->
<!--[if (IE 5)]><p>You are using IE 5 (any version).</p><![endif]-->
<!--[if (gte IE 5.5)&(lt IE 7)]><p>You are using IE 5.5 or IE 6.</p><![endif]-->
<!--[if lt IE 5.5]><p>Please upgrade your version of Internet Explorer.</p><![endif]-->
<!--[if true]>You are using an <em>uplevel</em> browser.<![endif]-->
<![if false]>You are using a <em>downlevel</em> browser.<![endif]>
<!--[if true]><![if IE 7]><p>This nested comment is displayed in IE 7.</p><![endif]>
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