3.15 The wrapper library
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Availability::- use_module(library(http/http_wrapper)).
Sourcehttp_relative_path(+AbsPath, -RelPath)
Convert an absolute path (without host, fragment or search) into a path relative to the current page, defined as the path component from the current request (see http_current_request/1). This call is intended to create reusable components returning relative paths for easier support of reverse proxies.

If ---for whatever reason--- the conversion is not possible it simply unifies RelPath to AbsPath.