Fixed bug #72586: Document that order of characters is important

reference/datetime/datetimeimmutable/createfromformat.xml

@@ -41,6 +41,14 @@
       formatting options below. In most cases, the same letters as for the
       <function>date</function> can be used.
      </para>
+     <para>
+      The format is parsed from left to right, which means that in some
+      situations the order in which the format characters are present effects
+      the result. In in the case of <literal>z</literal> (the day of the year)
+      it is required that it is only used if a year has already been parsed,
+      for example through the <literal>Y</literal> or <literal>y</literal>
+      characters.
+     </para>
      <para>
       <table>
        <title>The following characters are recognized in the