In-Band Signaling as Standard
Any communications engineer will tell you that in-band signaling is a bad idea. In UNIX, it's often the only way of doing things. UNIX seems to have a strong philosophical objection to the idea of metadata. The UNIX file system doesn't even include a single bit to mark a file as hidden. Instead, UNIX uses a dot (.) at the start of a filename to mark it as hidden. When Mac OS was using 32-bit file type codes, and DOS-like systems were using a three-character file extension to identify file types, UNIX was embedding the file type in the filename.
In-band signaling is everywhere in UNIX. Everything is a file, so everything is a stream of bytes. While other systems allow other metadata to be associated with files, UNIX just treats them as a long stream. This leads to control structures and data being intermingled because the way applications are connected to each other or to devices is by one pretending to be a file.