Struts Validation

[charmy jain]

hi,

i want add cutome validation into validator-rules.xml file of struts ? how it done ?
and

suppose :
i want to used zipCode validation into struts .

i write code into validation.xml for field mapping , write

code like

<field
property="zipCode"
depends="required,mask">
<arg key="inputForm.zipCode"/>
<var>
<var-name>mask</var-name>
<var-value>^\d{5}$</var-value>
</var>
</field>

so i want to understand what is meaning of "^\d{5}$" ,
and what is patteren of pass the mask value as variable ?

thanks