Jan Štětina

Includes custom HTML/CSS/JS code in the section on every blog in the network.
Very simple, but sometimes useful plugin.
After activation visit Network Admin –> Settings –> Multisite wp_head Code for setup. Nothing else is needed.
Developed for private use, but has perspective for more extensive usage. I can’t guarantee any support in the future nor further development, but it is to be expected. Kindly inform me about bugs, if you find any, or propose new features: <a href="mailto:zaantar@zaantar.eu?subject=[multisite-wphead-code]" rel="nofollow ugc">zaantar@zaantar.eu</a>.

Multisite wp_head Code

Includes custom HTML/CSS/JS code in the  section on every blog in the network.

Michael Torbert

This is the long description. No limit, and you can use Markdown (as well as in the following sections).
For backwards compatibility, if this section is missing, the full length of the short description will be used, and 
Markdown parsed.
A few notes about the sections above:
<ul>
<li>“Contributors” is a comma separated list of wp.org/wp-plugins.org usernames</li>
<li>“Tags” is a comma separated list of tags that apply to the plugin</li>
<li>“Requires at least” is the lowest version that the plugin will work on</li>
<li>“Tested up to” is the highest version that you’ve successfully used to test the plugin. Note that it might work on 
higher versions… this is just the highest one you’ve verified.</li>
<li>
Stable tag should indicate the Subversion “tag” of the latest stable version, or “trunk,” if you use <code>/trunk/</code> for 
stable.
Note that the <code>readme.txt</code> of the stable tag is the one that is considered the defining one for the plugin, so 
if the <code>/trunk/readme.txt</code> file says that the stable tag is <code>4.3</code>, then it is <code>/tags/4.3/readme.txt</code> that’ll be used 
for displaying information about the plugin. In this situation, the only thing considered from the trunk <code>readme.txt</code> 
is the stable tag pointer. Thus, if you develop in trunk, you can update the trunk <code>readme.txt</code> to reflect changes in 
your in-development version, without having that information incorrectly disclosed about the current stable version 
that lacks those changes — as long as the trunk’s <code>readme.txt</code> points to the correct stable tag.
If no stable tag is provided, it is assumed that trunk is stable, but you should specify “trunk” if that’s where 
you put the stable version, in order to eliminate any doubt.
</li>
</ul>
<h3>Arbitrary section</h3>
You may provide arbitrary sections, in the same format as the ones above. This may be of use for extremely complicated 
plugins where more information needs to be conveyed that doesn’t fit into the categories of “description” or 
“installation.” Arbitrary sections will be shown below the built-in sections outlined above.
<h3>A brief Markdown Example</h3>
Ordered list:
<ol>
<li>Some feature</li>
<li>Another feature</li>
<li>Something else about the plugin</li>
</ol>
Unordered list:
<ul>
<li>something</li>
<li>something else</li>
<li>third thing</li>
</ul>
Here’s a link to <a href="https://wordpress.org/" title="Your favorite software" rel="ugc">WordPress</a> and one to <a href="http://daringfireball.net/projects/markdown/syntax" title="Markdown is what the parser uses to process much of the readme file" rel="nofollow ugc">Markdown’s Syntax Documentation</a>. 
Titles are optional, naturally.
Markdown uses email style notation for blockquotes and I’ve been told:
<blockquote>
Asterisks for emphasis. Double it up for strong.
</blockquote>
<pre><code><?php code(); // goes in backticks ?>
</code></pre>

Clean WP Head

Here is a short description of the plugin.  This should be no more than 150 chars.  No markup here.

Multisite wp_head Code vs Clean WP Head