Typo found by online editor user

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@325203 c90b9560-bf6c-de11-be94-00142212c4b1

language/types/null.xml

@@ -59,7 +59,7 @@ $var = NULL;
   <title>Casting to <literal>NULL</literal></title>
 
   <para>
-   Casting a variable to <type>null</type> using <literal>(unset) $var</literal>
+   Casting a variable to <type>null</type> using <literal>unset($var)</literal>
    will <emphasis>not</emphasis> remove the variable or unset its value.
    It will only return a &null; value.
   </para>

language/types/string.xml

@@ -1030,7 +1030,7 @@ echo "\$foo==$foo; type is " . gettype ($foo) . "<br />\n";
    may be problematic.
   </para>
   <para>
-   Of course, in order to useful, functions that operate on text may have to
+   Of course, in order to be useful, functions that operate on text may have to
    make some assumptions about how the string is encoded. Unfortunately, there
    is much variation on this matter throughout PHP’s functions:
   </para>

reference/http/setup.xml

@@ -40,7 +40,7 @@
     A library version equal or greater than <emphasis>v1.2.2</emphasis> is required.
    </para>
    <para>
-    <emphasis>Content type quessing</emphasis> can be enabled by
+    <emphasis>Content type guessing</emphasis> can be enabled by
     building this extension with <link xlink:href="&url.libmagic;">libmagic</link> support
     (<literal>--with-http-magic-mime</literal>).
    </para>