If you are sure that your 'DirName' column only contains valid characters (for a directory), and that it is unique, then you can edit the file 'admin/Plugins/PageBuilder.pm'.
Near the beginning of the file, add the bit in red:
directory => [qw/LinkID Full_Name CategoryID DirName/] },
...
Ivan
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Iyengar Yoga Resources / GT Plugins
Near the beginning of the file, add the bit in red:
Code:
$PAGEBUILDER_FIELDS = { link => { filename => [qw/LinkID/], directory => [qw/LinkID Full_Name CategoryID DirName/] },
...
Ivan
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Iyengar Yoga Resources / GT Plugins