Here is a list of all documented struct and union fields with links to the struct/union documentation for each field:

range : L_Bilateral
range_stdev : L_Bilateral
rankhaus : JbClasser
rch : L_Recog
rcha : L_Recog
red : RGBA_Quad
redfactor : L_Dewarp, L_Dewarpa
reduction : L_Bilateral
refcount : Box, Boxa, CCBord, DPix, FPix, FPixa, L_Bytea, L_Dna, Numa, Pix, Pixa, Pta, Sarray
refpage : L_Dewarp
res : L_Compressed_Data
rightcurv : L_Dewarp
rightslope : L_Dewarp
rootname : GPlot