Suggested tags to do:

=== All tags have 'var' for storing output ===
=== jstlVar is a variable in EL. ${jstlVar} is that variable evaluated ===

<un:catch type="java.sql.SQLException">
  ...
</un:catch>

<un:instanceOf target="foo" type="java.sql.SQLException">
  ...
</un:instanceOf>

[This would most likely be implemented into JSTL as the EL instanceof operator]

<un:collection type="java.util.ArrayList">
  <un:element value="${someVar}"/>
<un:collection/>
<un:collection+ var="foo">
  <un:pair key="Alice" value="2282828"/>
</un:collection+>
<un:collection- var="foo">
  <un:pair key="Alice"/>
  <un:pair value="92"/>
  <un:pair key="Bob" value="9191"/>
</un:collection->
<un:map var="foo" type="java.util.HashMap">
  <un:pair key="Bob" value="${someOtherVar}"/>
</un:map>
<un:map+ var="foo">
  <un:pair key="Alice" value="2282828"/>
</un:map+>
<un:map- var="foo">
  <un:pair key="Alice"/>
  <un:pair value="92"/>
  <un:pair key="Bob" value="9191"/>
</un:map->

<un:invoke method="foo" target="jstlVar">
  <un:arg value="${el.string}"/>
</un:invoke>

<un:var attribute="Person.URL"/>
<un:var attribute="name" target="jstlVar"/>

<!-- more likely for String taglib -->
<un:equalsIgnoreCase var="jstlVar" lhs="${bob}" rhs="${alice}"/>
[This could be implemented in JSTL's EL as a ~= operator]
[Akin to the mathematical operator 'equivalent to'  2 ~ on top of each other]
[Might be useful for float comparison too]

<un:equals ignoreCase="true|false" var="jstlVar" lhs="${someObj.property" rhs="boat"/>

<un:finishPage/>