In the SASLib.jl package, most constants are defined in the constants.jl file located at https://github.com/tk3369/SASLib.jl/blob/master/src/constants.jl.

Here's a fragment of the code:

# default settings
const default_chunk_size = 0
const default_verbose_level = 1 

const magic = [
         b"x00x00x00x00x00x00x00x00" ;
         b"x00x00x00x00xc2xeax81x60" ;
         b"xb3x14x11xcfxbdx92x08x00" ;
         b"x09xc7x31x8cx18x1fx10x11" ]

const align_1_checker_value = b"3"
const align_1_offset = 32
const align_1_length = 1
const align_1_value = 4

Using these constants allows the file-reading functions to perform well.