uri: Add description to all Exceptions

Author: TimWolla

reference/uri/uri.invaliduriexception.xml

@@ -7,6 +7,7 @@
   <section xml:id="uri-invaliduriexception.intro">
    &reftitle.intro;
    <simpara>
+    Indicates that a given URI is invalid or that an operation would result in an invalid URI.
    </simpara>
   </section>
 

reference/uri/uri.urierror.xml

@@ -7,6 +7,7 @@
   <section xml:id="uri-urierror.intro">
    &reftitle.intro;
    <simpara>
+    The base class for <type>Error</type>s that occur during processing of URIs.
    </simpara>
   </section>
 

reference/uri/uri.uriexception.xml

@@ -7,6 +7,7 @@
   <section xml:id="uri-uriexception.intro">
    &reftitle.intro;
    <simpara>
+    The base class for <type>Exception</type>s that occur during processing of URIs.
    </simpara>
   </section>
 

reference/uri/uri.whatwg.invalidurlexception.xml

@@ -7,6 +7,9 @@
   <section xml:id="uri-whatwg-invalidurlexception.intro">
    &reftitle.intro;
    <simpara>
+    Indicates that a given URL is invalid or that an operation would
+    result in an invalid URL according to the
+    <link xlink:href="&url.url.whatwg-url;">WHATWG URL Standard</link>.
    </simpara>
   </section>