Markup in the Monastery

Nesting: Check for proper nesting. For example, if you open a paragraph tag, close it before beginning a blockquote or code segment. And that leads us directly to the next important pair of tags.

Code:

Use code tags, <c>..</c> (or <code>...</code>), to post code and data. Doing so preserves your indentation, blank lines and those symbols for which use of character-entities is conventional elsewhere. Char-entities are discussed further, below

A typical use would be to cut'n'paste your code into a PM node Code tags cause the code (or data) they enclose to appear in a distinguishable font. If you have turned on line-numbering in the section on "Code Listing Setings" in Display Settings the code lines will be numbered. The following is inside <c>...</c> tags.

#!/usr/bin/perl
use warnings;
use strict;
use (some module);

if (some condition) {
    do something;
    and something more; # with a comment to make this a very, very lon
+g line which will wrap in many browser windows, absent a gigundo moni
+tor and so on. If you don't have auto code wrap on in "code," you'll 
+see a red plus sign and a lack of line number on the continuations af
+ter wrapping is performed (sometimes at unfortunate points, as can be
+ seen in this instance, if you don't have auto code wrap turned on.
}
else {
    &whatever; # Note below
}

sub whatever {
  do something;
}
[download]

Note the download link, above. It appears after each stand-alone code block and allows readers to retrieve the code or data, without the line numbers.

Note that in line 11 the "&" did NOT have to be written as a character entity (&amp;). If you're not seeing line numbering, see that setting in Display Settings.

<pre> vs. <code>

At first blush, the <pre> ...</pre> pair may look like an alternative to code tags... BUT DON'T USE IT HERE chiefly because <pre>...</pre> tags will not persuade the Monastery to provide a download link for the contents of the <pre>... and while it is now supposed to wrap lines that are too long for the viewer's browser window, there are ways Monks could use CSS that would defeat that. So, please. don't use <pre>...</pre> except to deal with exceptional cases... like that in the next paragraph (which still needs examples of using pre inside a long stretch of code).

Exception: non-ASCII characters inside the ... may magically display as unrendered entities (i.e., as question-marks) instead of the character you expected, whereas inside <pre> ...</pre>, they may work as expected. (Thanks, pryrt).

More untoward or problematic markup

Inserting a <br> tag forces a newline at the point at which it's inserted. Monastery documents differ on its acceptability but in the form in this sentence, it generally works... while alternates, like XHTML's <br /> do NOT work.

Using <div>...</div> tags is NOT deprecated, but unless you're expert in .html, you probably shouldn't use them here.

<font (something="something")>... </font> tags are frowned upon. Don't use them except in extraordinary circumstances.

Character Entities

Please read carefully the hints which appear below the text entry box when you're creating a node. Outside code tags

Appendix

If you are a logged-in user, you have Display Settings which you can check or change. See particularly the section HTML Related Options. It is highly recommended that you check the checkbox and set the two other options to their maximum values (3 and 4, respectively). These will tell you quite clearly when you omit a required tag, and will help when you bork tag nesting rules.

Most of the tags discussed above should be used in pairs (that is, <tag>... </tag>. While some of the other tags addressed in this node will DWIM even if you fail to close them, the <b>, <i>, and <tt> tags will not, nor will some "block level" tags like <ol>.

A table listing all PM-approved html and arguments is available for those who wish to delve deeper.

Beware of using your browser's "view page source" feature to see how a writeup has been formatted. Not only are you viewing a node after it has been processed by PerlMonks (turning What shortcuts can I use for linking to other information? into actual links, for example), but many browsers do additional processing on received pages, such as inserting missing closing tags.

In the interest of brevity and simplicity, some statements above are oversimplified... and some do NOT apply to the CB, for which see PerlMonks Approved Chatter HTML Tags.

...and finally

None of this will be much help if your content is unclear. Use an explanatory title, standard spelling, grammar, and punctuation. If posting a question, explain exactly what your problem is (and include warnings and error messages, verbatim, if received). Tell us what your input is in a separate code block or as a <DATA> section at the end of your code. Be explicit about the expected output, unless that's utterly unambiguous, and tell us how what you're getting, if anything, deviates from your expectations or desires.

How do I post a question effectively?, Before You Post ... and On asking for help address many valuable points. If you're new to the Monastery, you'll profit greatly — EVEN IF YOU'RE IN A RUSH TO GET AN ANSWER — by reading these. And, oh yes, remember, "Your 'urgent need' is not our emergency."