Default image file suffix. Appended to the catalog::Path (or catalog::MaskPath) field value if the path does not include a file suffix
A file suffix consists of a period and one or more characters between the period and the end of the string. The suffix is appended to the http path, if the path does not resolve to a catalog entry, and if the last path element does not include a file suffix.
Text string. Must include a leading ‘.’ and one or more characters.
default::DefaultExt if not defined. If defined but empty, no default suffix is applied to image names when using this catalog.
catalog::Path , catalog::MaskPath