Make Custom Block Properties Required

To ensure that specific input parameters are supplied to a macro being used as a custom block in Wires, add the macro metadata element <required> to <parameter> within <parameters> and make the value true.

<macros xmlns="http://www.open-mashup.org/schemas/v1.0/EMML"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.openmashup.org/schemas/v1.0/EMML/..
/schemas/EMMLPrestoSpec.xsd"
domain="myBlocks">

<macro name="helloWorld"
xmlns:presto="http://www.jackbe.com/v1.0/EMMLPrestoExtensions"
xmlns:macro="http://www.openmashup.org/schemas/v1.0/EMMLMacro">
<presto:macro-meta>
<block usage="Wires">
...
</block>
<parameters>
<parameter name="aString">
<label>Your name</label>
<help>Tooltip for this property</help>
<required>true</required>
</parameter>
...
</parameters>
</presto:macro-meta>
....
</macro>
...
</macros>

If there are properties marked as required, Wires prevents users from running the block to preview results until all required properties are set.