CLHS: Section 19.2.2.2.3

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## 19.2.2.2.3 :UNSPECIFIC as a Component Value

If `:unspecific` is the value of a pathname component, the component is considered to be ``absent'' or to ``have no meaning'' in the filename being represented by the pathname.

Whether a value of `:unspecific` is permitted for any component on any given file system accessible to the implementation is implementation-defined. A conforming program must never unconditionally use a `:unspecific` as the value of a pathname component because such a value is not guaranteed to be permissible in all implementations. However, a conforming program can, if it is careful, successfully manipulate user-supplied data which contains or refers to non-portable pathname components. And certainly a conforming program should be prepared for the possibility that any components of a pathname could be `:unspecific`.

When reading[1] the value of any pathname component, conforming programs should be prepared for the value to be `:unspecific`.

When writing[1] the value of any pathname component, the consequences are undefined if `:unspecific` is given for a pathname in a file system for which it does not make sense.

## 19.2.2.2.3.1 Relation between component values NIL and :UNSPECIFIC

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- PATHNAME-UNSPECIFIC-COMPONENT:NEW-TOKEN

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