minor #3006 update docs for for loop with conditional to reference filter filters (shieldo)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead (closes #3006).

Discussion
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update docs for for loop with conditional to reference filter filters

I don't know if there needs to be the same emphasis for this case as there's no special syntax for this any more? This PR assumes the same emphasis.

Commits
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b905e023 update docs for for loop with conditional to reference filter filters

doc/tags/for.rst

@@ -87,6 +87,13 @@ Variable              Description
 Adding a condition
 ------------------
 
+.. tip::
+
+    As of Twig 2.10, use the :doc:`filter <../filters/filter>` filter instead,
+    or an ``if`` condition inside the ``for`` body (if your condition
+    depends on a variable updated inside the loop and you are not using the
+    ``loop`` variable).
+
 Unlike in PHP, it's not possible to ``break`` or ``continue`` in a loop. You
 can however filter the sequence during iteration which allows you to skip
 items. The following example skips all the users which are not active: