Fix references, add helpful comments

examples/StringChecker.php

@@ -1,31 +1,36 @@
 <?php
 namespace Psalm\Example\Plugin;
 
-use PhpParser;
 use Psalm\Checker;
 use Psalm\Context;
+use Psalm\CodeLocation;
 
 /**
  * Checks all strings to see if they contain references to classes
- * and, if so, checks that those classes exist
+ * and, if so, checks that those classes exist.
+ *
+ * You will need to add `"nikic/PHP-Parser": ">=3.0.2"` to your 
+ * composer.json.
  */
 class StringChecker extends \Psalm\Plugin
 {
     /**
-     * checks an expression
-     * @param  PhpParser\Node\Expr  $stmt
-     * @param  Context              $context
-     * @param  CodeLocation        $file_name
-     * @param  array<string>        $suppressed_issues
+     * Checks an expression
+     *
+     * @param  \PhpParser\Node\Expr  $stmt
+     * @param  Context               $context
+     * @param  CodeLocation          $code_location
+     * @param  array<string>         $suppressed_issues
      * @return null|false
      */
     public function checkExpression(
-        PhpParser\Node\Expr $stmt,
+        \PhpParser\Node\Expr $stmt,
         Context $context,
         CodeLocation $code_location,
         array $suppressed_issues
     ) {
         if ($stmt instanceof \PhpParser\Node\Scalar\String_) {
+            // Replace "Psalm" with your namespace
             $class_or_class_method = '/^\\\?Psalm(\\\[A-Z][A-Za-z0-9]+)+(::[A-Za-z0-9]+)?$/';
 
             if (preg_match($class_or_class_method, $stmt->value)) {