new-line exists in rebol / red for block what about tabs?

Question

I can't find new-tab whereas there is new-line so how do you preserver tabs in blocks ?

    help new-line
    USAGE:
         NEW-LINE position value

    DESCRIPTION: 
         Sets or clears the new-line marker within a block or paren. 
         NEW-LINE is a native! value.

    ARGUMENTS:
         position     [block! paren!] "Position to change marker (modified)".
         value         "Set TRUE for newline".

    REFINEMENTS:
         /all         => Set/clear marker to end of series.
         /skip        => Set/clear marker periodically to the end of the series.
            size         [integer!] 

    RETURNS:
         [block! paren!]

Answer 1

There is one newline flag per-cell in arrays ("any-block!"s), which indicates whether or not the molding process should put out a newline before that value.

Indentation is driven only from these flags. Indentation starts at the first newline flag, and further newlines will each align to that level, with an outdent at the end of the block if any newlines/indents occurred.

>> data: [a b c]

>> new-line next data true

>> data
== [a 
   b c
]

Note there are 4 "candidate positions" for newlines inside the block [a b c] (e.g. the positions are [* a * b * c *]). Yet there are only three value cells, with a newline marker indicating a desire to output a newline before that cell. Lacking anywhere to put the fourth newline signal, the decision in Rebol2 and Red is to implicitly put the closing bracket on its own line if there were any newline markers processed.

I've previously mentioned that it's non-obvious exactly how "out-of-band" information like this gets managed in the face of series modifications. It helps to work through your expectations. Even worrying about just one bit there is a lot of nuance, such as when you say:

compose [
    1 + (block1)
    (block2)
]

How should newline markers be merged, between what's in the COMPOSE and what's in the spliced data itself? That's just the logic related to one bit. Putting in some "indentation count" would introduce many more questions. Plus, there's not a lot of bits to spare for that count: one of the "rules of the game" is to keep things down to just 4 platform pointers per value cell.

Expanding the formatting features isn't too likely. One feature request that the tail get its own newline marker was accepted for open source Rebol3, but rejected by Red. I wouldn't expect to see much more done in this area.