How to modify a website's source code

Third-party plugins can grant you easier access to the "essence" of your website and make inserting codes/strings easier. There are many plugins, for many purposes. For example, one of them is the Headers and Footers plugin which you may use to add code to the header and/or footer section. You may download and install it from here.

By default, Joomla doesn’t allow use of any special styles or syntax in its post and module titles. Luckily, there is a workaround for this restriction.

Follow the advice in the article on gavick.com, which should help you add your custom strings.

The Squarespace platform has built-in features for adding custom code, like Code Block, CSS Editor, and Code Injection. This article by Squarespace will show you how to add your own different types of custom code and there you may find a video tutorial:

Advanced Customizations & Adding Custom Code

Note: You may check the full guide on adding codes here of Squarespace's website.

Follow the steps below to add a custom code:

1. Click Add on the left side of the editor and click More.
2. Click on HTML Code, or drag it to the relevant location on your page.
3. Enter the custom HTTPS code and click Apply. 

Note: Feel free to read the full guide on adding custom codes on Wix's website.

There are three options to add code/string to your blog:

1. In a widget/gadget.
   These can be placed in any location the Layout gives you access to - usually into the header, footer or sidebar.
   
   
2. Inside a specific post (or page).
   This means that the effect of the code will be shown every time the post is viewed.
   
   
3. In the blog's layout theme.
   This gives you most control over where and how the item appears, but is also the hardest.
   
   

To add a code in widget:

1. Prepare the code.
2. In Blogger, choose Layout > Add a Gadget > HTML-Javascript
3. Select the gadget created by Blogger which is in the Basic list.
4. Paste the code into the Contents field.
5. Enter a title (optional)
6. Press Save. 
7. Drag-and-drop the new gadget to where you want it to appear.
8. Save the layout.
   
   

To add a code in a post:

1. Prepare the code.
2. Copy the code from the third party site.
3. Go to Blogger and Edit the Post (or Page) that you want to put it on.
4. Switch into HTML mode.
5. Paste the code in at the place where you want the item to go.
6. Save the change.

To add a code in a theme:

1. Edit your theme.
2. Put the code where you like it to be.
3. Preview the change, to make sure it works.
4. Save the theme.

Note: For more detailed explaination, feel free to check the article on this blog

1. Log in to your account.
2. Select your Tumblr blog's name at the top of the Tumblr dashboard and click Customize Appearance located on the right side of the screen.
3. Click Theme at the top of the Customize page;
4. Click the Use custom HTML button located just under those themes and your blog's current HTML code will appear.
5.  Click anywhere in the code, press to create a new line and insert your HTML code.
6. Click "Update Preview" to preview the changes. You may need to click "Theme" again to hide the HTML code to see the current theme. (optional) click on "Theme" again, if you need to alter the code again.
7. Click "Save and Close" to save the changes.

Source: http://smallbusiness.chron.com/insert-html-tumblr-30154.html

This article on Wordpress describes how to add codes safely to your Wordpress website. Basically they recommend wrapping your code in these tags:

[code language="css"]
your code here
[/code]

Note: CSS can be replaced with other languages, including actionscript3, bash, clojure, coldfusion, etc.

You may read more detailed instructions here.

1. Open the Shopify Admin panel.
2. Click on Sales Channels and select Online Store.
3. Click on Themes and then on the three dots (...).
4. Click on Edit HTML/CSS from the list.
5. Open the appropriate HTML file and paste the plugin's code (or other custom code) into the file in the appropriate location.
6. Click on Save to save the changes and then on Preview to preview them.

Source: support.zendesk.com

Look for the app/design/frontend/{template}/page/html/head.phtml file where {template} is the name of your active Magento template. If this file doesn’t exist, then you will need to check if the app/design/frontend/{template}/default/page/html/head.phtml file exists. It is recommended to place the code before the </head> section of the file.

Note: If the template files mentioned above don't exist, you need to copy the base head.phtml into your custom template. Copy the app/design/frontend/default/page/html/head.phtml file from your default base template to your custom template folder at app/design/frontend/{template}/page/html/head.phtml. You can then open the file and place the chat code before the </head> tag as recommended.

Source: chatstack.com

If you want to add custom PHP code in Magento cms page:

1. Log into the Magento admin panel.
2. Go to "CMS -> Pages".magento cms - menu
3. Click "Add new page".magento cms - page info
4. Enter the title of the page and enter the URL key.
5. Activate the page by selecting "Status".
6. Add the content of the page in HTML format.
7. In the "Design" inset you can edit the page layout.
8. In the tab "Meta data" you need to enter a page description and keywords.
9. Click "Save Page" to save the changes and a new page should appear in the grid.

Source: webinse.com

1. Go to settings and click on <> Code Injection.
2. Paste the following code in the footer, :
   
   <script src="//cdn.rawgit.com/google/code-prettify/master/loader/run_prettify.js?skin=sons-of-obsidian" type="text/javascript">
   
   
3. Once you've added that script to your footer, you simply need to use the following code to insert source code:

<pre class="prettyprint linenums"><code>function someCode(){
    // this is code
}
</pre></code>

Note: If you intend to add <script/> tags using this process: you will have to HTML encode the first < on the line, or Ghost will think you are trying to embed a script. So, in the example above, this is what the first line looks like:

<pre class="prettyprint linenums lang-htm"><code>&lt;script src=...</script></code></pre>

The video tutotial available on drupalize.me , will teach you how to add custom code on Drupal.

Note: In order to be able to watch the video, you need to sign up first.

The following documentation should teach you how to manage Javascript in Drupal:
https://www.drupal.org/node/756722

The following documentation is CSS-related:
https://www.drupal.org/node/341246

If you are interested in PHP, you can find all the info you need here:
https://www.drupal.org/docs/7/howtos/add-php-code-to-the-body-of-a-drupal-7-block

The article on Typo3, should help you add the code you wanted, in an easy way. Basically, you need to use the Plain HTML content element for this purpose.

http://www.typo3support.com/typo3-manual-4x/4-elements-of-contents/47-plain-html/

The article on chami.com should enable you to add custom code in an easy way.