Neutrino's CD-ROM filesystem provides transparent access to CD-ROM media, so you can treat CD-ROM filesystems as though they were POSIX filesystems. This transparency lets processes operate on CD-ROM files without any special knowledge or work on their part.
The fs-cd.so shared object provides filesystem support for the ISO 9660 standard as well as a number of extensions, including Rock Ridge (RRIP), Joliet (Microsoft), and multisession (Kodak Photo CD, enhanced audio). This shared object is automatically loaded by the devb-* drivers when mounting an ISO-9660 filesystem.
The CD-ROM filesystem accepts any characters that it sees in a filename; it's read-only, so it's up to whatever prepares the CD image to impose appropriate restrictions. Strict adherence to ISO 9660 allows only 0-9A-Z_, but Joliet and Rockridge are far more lenient.