:sig
bool path_is_within(String path, String root)

:params
path : path to test
root : directory that should contain it
return value : true if `path` is inside `root`

:content
Reports whether `path` lies inside `root`. It resolves both paths to their canonical form (like `path_real()`), so they must exist and `..` traversal is collapsed first. Use it to reject path-traversal attempts before opening user-supplied paths.

:example
mkdir("/tmp/doc-within");
file_put_contents("/tmp/doc-within/app.txt", "x");
print(path_is_within("/tmp/doc-within/app.txt", "/tmp/doc-within") ? "inside" : "outside", " / ");
print(path_is_within("/tmp/doc-within/../doc-within/app.txt", "/tmp/doc-within") ? "inside" : "outside", "\n");
dir_remove("/tmp/doc-within", true);

:see
>sys
path_real
expand_path