This attribute toggles the activation of PHPTAL debugging for the content of the tag it is defined in.
To debug errors in macros called across templates you need to add
phptal:debug in template which defines the macro, not the one which uses it.
The debug mode stores information like filename and source line number in the template, so exceptions thrown by incorrect path access will contain more information about where they where thrown.
<html> <head> … </head> <body> <div id="menu"> … </div> <div id="leftPane" phptal:debug="" tal:comment="this div seems buggy, keep trace of where errors are thrown"> … </div> </body> </html>