Updated Calling functions (markdown)

Functions.md

@@ -1,3 +1,25 @@
+# Parameters with default values must appear last in functions
+
+It is considered good practice to make parameters with default values last in function declarations.
+
+<details><summary>Example</summary><div><br>
+
+**Bad**
+
+```PHP
+function showTitle($duration = 60000, $title) { ... }
+```
+
+**Good**
+
+```PHP
+function showTitle($title, $duration = 60000) { ... }
+```
+
+</div></details><br>
+
+_Reference_: [`PEAR.Functions.ValidDefaultValue`](https://github.com/squizlabs/PHP_CodeSniffer/blob/master/src/Standards/PEAR/Sniffs/Functions/ValidDefaultValueSniff.php)
+
 # Calling functions
 
 Function calls must follow a few rules in order to maintain readability throughout the project: