Here's an example of an edit box control bound to a date field with a default value:
<xp:inputText id="Date" value="#{document.Date}" defaultValue="#{javascript:@Today()}">
<xp:this.converter>
<xp:convertDateTime type="date" />
</xp:this.converter>
<xp:dateTimeHelper id="dateTimeHelper2" />
</xp:inputText>