Gets or sets a value that specifies the default extension string to use to filter the list of files that are displayed.
Assembly: PresentationFramework (in PresentationFramework.dll)
The extension string must contain the leading period. For example, set theproperty to ".txt" to select all text files.
By default, the AddExtension property attempts to determine the extension to filter the displayed file list from the Filter property. If the extension cannot be determined from the Filter property, will be used instead.
Available since 3.0