Expression Editor needed in Document Properties/Properties dialogue

Given that Property Controls such as a list box can contain Custom Expressions, employing Document Properties is a useful method to consistently populate those controls and expressions across multiple dashboard pages. 

It is not uncommon to have the same control on multiple pages.  If changes to a Custom Expression are necessary it requires that all the duplicate property control's  expressions be maintained one-by-one unless you use a Document Property to hold all the Custom Expressions centrally and refer to them in the property controls only by Document Property.

A similar case can be made for filter expressions that exist on multiple visualizations.  The best way to develop is using document properties to hold the filter expressions.  It centralizes maintenance and speeds development of dashboards.

The only drawback is that the Expression Editor is not available in the Document Properties/Properties dialogue where you edit the value of the Property.  All we are provided is a small text box.  At the very least that needs to be larger, but what is really needed is access to the Custom Expression Editor directly from the Document Property editor.  A button that allowed you to save the expression to the property even if not syntactically correct would be useful.  Often we build up a complete expression from multiple document properties.