[Rd] filenames with special characters in the R/ directory of a package?

[blue sky]

According to R-exts.pdf (page 3):
For maximal portability filenames should only
contain only ASCII characters not excluded already (that is
A-Za-z0-9._!#$%&+,;=@^(){}’[]

I have some files with special characters like '[' and '%' e.g.
'[.set.R'. I also have some functions that also have those special
characters defined in those files exported in NAMESPACE.

I use the following command to install. And I get no warning or errors.

R CMD INSTALL -d -l my_custom_dir my.pkg

I then load the package. I get the following errors and warnings. I
changed a file to one without these special characters. Then the
corresponding warning/error disappears. Is it the case that there
should never be files with special characters as names?

> library(my.pkg)
Error in namespaceExport(ns, exports) :
 undefined exports: %is%
In addition: Warning message:
S3 methods ‘[.set’ were declared in NAMESPACE but not found
Error: package/namespace load failed for 'my.pkg'