doc: fix typo and tighten wording in error sections

Changes:
- Removed superfluous "when possible"
- Fixed typo in "documentationt"
- Added missing comma
- Moved definition of error union type up to first sentence

doc/langref.html.in

@@ -2864,18 +2864,18 @@ const err = (error {FileNotFound}).FileNotFound;
       assert to make sure the error value is in fact in the destination error set.
       </p>
       <p>
-      The global error set should generally be avoided when possible, because it prevents
-      the compiler from knowing what errors are possible at compile-time. Knowing
-      the error set at compile-time is better for generated documentationt and for
-      helpful error messages such as forgetting a possible error value in a {#link|switch#}.
+      The global error set should generally be avoided because it prevents the
+      compiler from knowing what errors are possible at compile-time. Knowing
+      the error set at compile-time is better for generated documentation and
+      helpful error messages, such as forgetting a possible error value in a {#link|switch#}.
       </p>
       {#header_close#}
       {#header_close#}
       {#header_open|Error Union Type#}
       <p>
-      Most of the time you will not find yourself using an error set type. Instead,
-      likely you will be using the error union type. This is when you take an error set
-      and a normal type, and create an error union with the <code>!</code> binary operator.
+      An error set type and normal type can be combined with the <code>!<code>
+      binary operator to form an error union type. You are likely to use an
+      error union type more often than an error set type by itself.
       </p>
       <p>
       Here is a function to parse a string into a 64-bit integer:
@@ -6033,4 +6033,3 @@ hljs.registerLanguage("zig", function(t) {
     </script>
   </body>
 </html>
-