Add missing @return $this annotations

Author: nicolas-grekas

Diff for: XPath/XPathExpr.php

@@ -43,6 +43,9 @@ public function getElement(): string
         return $this->element;
     }
 
+    /**
+     * @return $this
+     */
     public function addCondition(string $condition): self
     {
         $this->condition = $this->condition ? sprintf('(%s) and (%s)', $this->condition, $condition) : $condition;
@@ -55,6 +58,9 @@ public function getCondition(): string
         return $this->condition;
     }
 
+    /**
+     * @return $this
+     */
     public function addNameTest(): self
     {
         if ('*' !== $this->element) {
@@ -65,6 +71,9 @@ public function addNameTest(): self
         return $this;
     }
 
+    /**
+     * @return $this
+     */
     public function addStarPrefix(): self
     {
         $this->path .= '*/';