Qindex Programming Tips
61 [Quick Reference] comments
written by Qindex at 2006-10-29 23:52 /


 CSS 2
Comments begin with the characters "/*" and end with the characters "*/". They may occur anywhere between tokens, and their contents have no influence on the rendering. Comments may not be nested.
CSS also allows the SGML comment delimiters ("<!-- " and "-->") in certain places, but they do not delimit CSS comments. They are permitted so that style rules appearing in an HTML source document (in the STYLE element) may be hidden from pre-HTML 3.2 user agents.

HTML comments have the following syntax:

<!-- this is a comment -->
<!-- and so is this one,
    which occupies more than one line -->

White space is not permitted between the markup declaration open delimiter("<!") and the comment open delimiter ("--"), but is permitted between the comment close delimiter ("--") and the markup declaration close delimiter (">"). A common error is to include a string of hyphens ("---") within a comment. Authors should avoid putting two or more adjacent hyphens inside comments.
Information that appears between comments has no special meaning (e.g., character references are not interpreted as such).
Note that comments are markup.

[Definition: Comments may appear anywhere in a document outside other markup; in addition, they may appear within the document type declaration at places allowed by the grammar. They are not part of the document's character data; an XML processor MAY, but need not, make it possible for an application to retrieve the text of comments. For compatibility, the string "--" (double-hyphen) MUST NOT occur within comments.] Parameter entity references MUST NOT be recognized within comments.
[15]       Comment       ::=       '<!--' ((Char - '-') | ('-' (Char - '-')))* '-->'

An example of a comment:

<!-- declarations for <head> & <body> -->

Note that the grammar does not allow a comment ending in --->. The following example is not well-formed.

<!-- B+, B, or B--->

 JavaScript 1.3
// comment text
/* multiple line comment text */

// </script
/* </script */
will produce an error

 MySQL 4.0.4
The MySQL server supports the # to end of line, -- to end of line and /* in-line or multiple-line */ comment styles:

mysql> SELECT 1+1;     # This comment continues to the end of line
mysql> SELECT 1+1;     -- This comment continues to the end of line
mysql> SELECT 1 /* this is an in-line comment */ + 1;
mysql> SELECT 1+
this is a
multiple-line comment


The -- (double-dash) comment style requires you to have at least one space after the second dash.
Single-quote and double-quote characters are taken to indicate the beginning of a quoted string, even within a comment. If the quote is not matched by a second quote within the comment, the parser doesn't realise the comment has ended.
A semicolon is taken to indicate the end of the current SQL statement and anything following it to indicate the beginning of the next statement.

 PHP 4
PHP supports 'C', 'C++' and Unix shell-style comments.

// This is a one-line c++ style comment
/* This is a multi line comment
yet another line of comment */
# This is a shell-style comment

The "one-line" comment styles actually only comment to the end of the line or the current block of PHP code, whichever comes first.

<h1>This is an <?php # echo "simple"; ?> example.</h1>
<p>The header above will say 'This is an example'.

You should be careful not to nest 'C' style comments, which can happen when commenting out large blocks.

echo "This is a test"; /* This comment will cause a problem */

HTML code after // ?> WILL be printed: ?> skips out of the PHP mode and returns to HTML mode, and // cannot influence that.




Rem comment
' comment

[permission] read:Anonymous, comment:Anonymous, write:Webmaster, upload:Webmaster, manage:Webmaster