I support Julio's request with preference for a single-character to start a line comment. Percent sign, ! and C didn't work either. The attempt to introduce visual indentation (because renaming the task name in an editor renders the block useless), either with two explicit spaces per level of indentation like
<macro name="test">
<task name="addSmilesCodes">
structureColumn=Structure
</task>
<task name="calculateCompoundProperties">
propertyList=totalWeight logP
structureColumn=Structure
</task>
</macro>
or with tabulator breaks everything in this indented block, too (a subsequent block without indentation will perform well).