Update textarea.md

Added section on file:XX:url tags
Cleared up and added details about text formatting

Author: nep

docs/fieldtypes/textarea.md

@@ -21,7 +21,17 @@ Height of the editor in rows of text.
 
 ### Text Formatting
 
-Specifies how the entered-text will be formatted when rendered on the front-end. Choices include replacing each linebreak with a `BR` tag, automatically surrounding paragraphs with `P` tags, or Markdown processing. [Additional plugins](development/plugins.md) may be installed to provide more text formatting options.
+Specifies how the entered text will be formatted when rendered on the front-end. Choices include:
+
+* **None** - content will be output exactly as entered
+* [**Auto line break**](/general/text-formatting.html#auto-br) - simply replaces each linebreak with a `<br>` tag
+* [**Markdown**](/general/text-formatting.html#markdown) - processes content as Markdown and outputs HTML
+* **XML Encode** - content is formatted and escaped for safe use in an XML document like an RSS feed
+* [**XHTML**](/general/text-formatting.html#auto-xhtml) - Encloses paragraphs with `<p>` tags, adds curly quotes, and does other more advanced processing to make plain text into proper HTML while leaving any HTML intact.
+
+XHTML is an original EE formatting option and it is a good default for plain text that needs to be output as nice HTML, especially for text that contains some HTML as well.   [Additional plugins](development/plugins.md) may be installed to provide more text formatting options.
+
+NOTE: **Note:** To see the Markdown or XML Encode options, those add-ons on must be installed.
 
 ### Allow Override?
 
@@ -34,3 +44,23 @@ Either left-to-right, or right-to-left.
 ### Field Tools
 
 Show formatting buttons to make writing markup easier, show a smiley chooser, or show a file chooser button to easily insert images or links to files.
+
+## {file:XX:url} Tag / Inserting a File
+
+In a textarea field, when you add a file using the field tools, EE will insert code like this:
+
+Images
+
+    <img src="{file:XX:url}" alt="" height="200" width="200">
+
+Other Files
+
+    <a href="{file:xx:url}">other-file.pdf</a>
+
+When the field is output, EE will replace `{file:XX:url}` with the file's URL.
+
+With that tag in the content of the field, EE will also track the file as being used in this entry. This information is updated whenever an entry is saved with a field containing `{file:XX:url}`. If you reference an uploaded file directly by URL, EE will not track that the file is in use in that entry. This tracking is true for other field types as well, but those other field types often do not display the tag directly as `{file:XX:url}`.
+
+If your site is set to [Compatibility Mode](/control-panel/file-manager/file-manager.md#compatibility-mode) for backwards compatibility with older add-ons, file references will instead look like `{filedir_X}filename.ext` and usage will not be tracked.
+
+