pkgname[-version]Here, pkgname is a label common to all versions of the package. It may contain any printable-ASCII character except for /, -, or NULL. A - character, if present, indicates the beginning of an optional version suffix. Versions consist of up to 5 .-delimited alphanumeric strings, limited to 10 characters each.
When the version is not present in a pkgspec, the package is said to have a null version. If a null version of a package coexists with other versions, the null version is considered the lowest version.