bug#19661: wrapping before window-width (new wrap-column text property?)

[Ivan Shmakov]

Package:  emacs
Severity: wishlist

        [As suggested in news:jwviogtdei4.fsf-monnier+emacs@gnu.org,
        news:87387w8r2j.fsf@violet.siamics.net, etc.; parts of the
        second message are reiterated below.]

        Please provide support for window-width-independent wrapping in
        the Emacs display engine; possibly by the means of a new
        wrap-column text property (and still perhaps complemented by a
        eponymous buffer-local variable), treated similarly to the likes
        of wrap-prefix.

        This feature could be used to display format=flowed (RFC 3676)
        MIME parts, as well as enriched-mode documents, documents using
        MediaWiki markup, SHR-rendered HTML documents, and pretty much
        any other kind of text which allows for /both/ wrappable and
        preformatted parts at the same time.

        It is already possible to influence the wrap width somewhat by
        setting the margin width variables (right-margin-width,
        left-margin-width) appropriately (see bug#4172, for instance.)
        The suggested wrap-column text property should probably have no
        effect on the window marginal areas, however.

        I admit that I know very little of the current Emacs display
        implementation.  However, it seems to me that wrap-column makes
        us one property closer to native multicolumn display (which’d
        warrant a separate wishlist bug report, though.)

        Consider, e. g.:

This is an example sentence with wrap-column set to 23.

This is yet another example sentence with line-prefix and wrap-prefix
both set to (space :align-to 25), – or something like that.

        From there, we may display it as follows:

This is an example
sentence with
wrap-column set to 23.

                         This is yet another example sentence with line-prefix
                         and wrap-prefix both set to (space :align-to 25), –
                         or something like that.

        Yet, provided that some other property is switched on, the Emacs
        display engine may decide to show it like this instead:

This is an example       This is yet another example sentence with line-prefix
sentence with            and wrap-prefix both set to (space :align-to 25), –
wrap-column set to 23.   or something like that.

        As already imagined in the preceding discussion, forward- and
        backward-char commands would then still follow the logical order
        of text in the buffer (that is: the “23” sentence, then the “25”
        one), while left-char, etc. would follow the visual order
        (assuming visual-order-cursor-movement.)

-- 
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