MRM (Motif Resource Manager)
The library that loads a Motif interface from a compiled UID file at run time: the other half of UIL, and the half the program actually links against.
UIL describes the widget tree in a text file, and the uil compiler turns it into a binary UID file. That is where MRM takes over. The program calls MrmInitialize, opens one or more UID files with MrmOpenHierarchy, and then pulls in whole windows or subtrees with MrmFetchWidget, which creates the widgets through Xt exactly as hand-written C would have. Callback names in the UIL file are bound to real function pointers with MrmRegisterNames, and individual strings, icons and colours can be fetched with MrmFetchLiteral.
The split gave you a hierarchy of UID files in which a translation or a new look was another file on the search path rather than another binary. The mechanism came over from DEC's XUI and stayed in Motif into the 2000s, but it is plainly a child of its era: binary resource files with no tool to inspect them, and a C API of a dozen functions that all return MrmSUCCESS or an error number. GUI builders like X-Designer preferred to generate C code outright.