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From Elxis Official Documentation

On Elxis 2009.1 or later you can create a new type of parameters on your module, bot or component XML parameters set. This is the folderlist. foldelist will list all existing folders in a given directory as a drop-down selection field. The value of the directory attribute is crucial and it is the relative path from the elxis root to the directory that you wish to display the folders list. If the given directory is invalid or does not exist the returned list will be empty. The results of the returned folders are being displayed always in LTR (Left-To-Right) direction. So you don't need to use the dir="ltr" attribute for the RTL (Right-To-Left) languages.

Usage examples:

<param name="tpl" type="folderlist" default="" directory="/templates" label="Select template" description="blah" />

<param name="gal" type="folderlist" default="" directory="/media/galleries" label="Select gallery" description="blah" />

As a sample usage of the folderlist parameter type see how you can load all elxis installed languages.