The arguments to "load" are, in order: target variable, offset to load from, number of bytes to load. The first argument must be an identifier of a symbol, the latter two are pre-compiled expressions.

The second argument may contain a label of the area, followed by ":" and then offset, or just a plain numeric expression, in which case it is an offset within entire output generated up to this point.

1/ what is meant by 'pre-compiled expressions', in the context of load and store CALM instructions

They perform elementary operations, mostly on a single unit of data, but at the same time they can perform many calculations in-place, because their arguments, with few exceptions, are pre-compiled expressions, similar to the second argument to "compute".

2/ typ., acceptable syntax for 2nd argument to load (or 1st argument to store), when need to refer to some specific addresss space area (i.e. using :: ...) ?
.. can u pls give concrete example

virtual
   Some_Area::
   db 'ABC'
end virtual

calminstruction demo
        local char
        load char, Some_Area: 0, 1
        display char+20h
end calminstruction

demo ; displays 'a'    

virtual at 1000h
   Some_Area::
   example db 'ABC'
end virtual

calminstruction demo address
        local char
        load char, Some_Area: address - 1 metadataof Some_Area, 1
        display char+20h
end calminstruction

demo example ; displays 'a'    

HEADER_LENGTH := 0

calminstruction patch offset*, str*
        store HEADER_LENGTH+offset, lengthof str, str
end calminstruction

db "Example text"

patch 7+1, "here"    

calminstruction (target) AreaContent? area*
        local string
        load string, area: 0, sizeof area
        publish target, string
end calminstruction

text AreaContent Some_Area
display text    

        file 'fasmg.exe'

        macro xorwithkey value*
                local   key
                virtual
                        key:: db string value
                end virtual
                xorout  key
        end macro 

        calminstruction xorout key_area
                local   offset, bytes, key, length
                compute length, sizeof key_area
                load    key, key_area:0, length
                compute offset, 0
            loop:
                check   offset = $%
                jyes    done
                check   offset + length <= $%
                jyes    xor
                compute length, $% - offset
                load    key, key_area:0, length
            xor:
                load    bytes, offset, length
                store   offset, length, bytes xor key
                compute offset, offset + length
                jump    loop
            done:
        end calminstruction

        xorwithkey 'fasmg'    

macro test
   virtual at 0
   (...)

   calm_inx

   (...)
   end virtual
end macro

calminstruction calm_inx
   local _tmp

   load _tmp,????,10 ; ??? load 10 bytes from current area ??? 
end calminstruction