| An empty namespace URI was specified.
|<code><pref:elem xmlns:pref=""/></code>
|- valign="top" scope="row"
|<code>XQST0087</code>
| An unknown encoding was specified. Note that the encoding declaration is currently ignored in BaseX.
|<code>xquery version "1.0" encoding "a b"; ()</code>
|- valign="top" scope="row"
|<code>XQST0088</code>
| An empty module namespace was specified.
|<code>import module ""; ()</code>
|- valign="top" scope="row"
|<code>XQST0089</code>
| Two variables in a <code>for</code> or <code>let</code> clause have the same name.
|<code>for $a at $a in 1 return $i</code>
|- valign="top" scope="row"
|<code>XQST0090</code>
| A character reference specifies an invalid character.
|<code>"�"</code>
|- valign="top" scope="row"
|<code>XQST0093</code>
| A module depends on itself. This may be triggered by a circular module definition.
|<code>import module ...</code>
|- valign="top" scope="row"
|<code>XQST0094</code>
| <code>group by</code> references a variable that has not been declared before.
|<code>for $a in 1 group by $b return $a</code>
|- valign="top" scope="row"
|<code>XQST0108</code>
| Output declarations may only be specified in the main module.
|Module: <code>declare output ...</code>
|- valign="top" scope="row"
|<code>XQST0109</code>
| The specified serialization parameter is unknown.
|<code>declare option output:unknown "..."; 1</code>
|}