summaryrefslogtreecommitdiffstats
path: root/docs/README.TRST
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 16:37:15 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 16:37:15 +0000
commitae5d181b854d3ccb373b6bc01b4869e44ff4d87a (patch)
tree91f59efb48c56a84cc798e012fccb667b63d3fee /docs/README.TRST
parentInitial commit. (diff)
downloadlynx-ae5d181b854d3ccb373b6bc01b4869e44ff4d87a.tar.xz
lynx-ae5d181b854d3ccb373b6bc01b4869e44ff4d87a.zip
Adding upstream version 2.9.0dev.12.upstream/2.9.0dev.12upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'docs/README.TRST')
-rw-r--r--docs/README.TRST158
1 files changed, 158 insertions, 0 deletions
diff --git a/docs/README.TRST b/docs/README.TRST
new file mode 100644
index 0000000..68b27af
--- /dev/null
+++ b/docs/README.TRST
@@ -0,0 +1,158 @@
+Tabular Support for Simple Tables
+=================================
+Some definitions first:
+
+* NO table support
+ What it says. :) Table related tags are treated like other
+ completely unrecognized tags.
+ Only listed for completeness, this does not describe Lynx.
+
+* MINIMAL table support
+ Table related tags are recognized, and are used to separate
+ the contents of different cells (by at least a space) and rows
+ (by a line break) visibly from each other.
+
+* LYNX minimal table support (LMTS)
+ The minimal table support as implemented by Lynx up to this point,
+ also includes the way ALIGN attributes are handled on TABLE, TR
+ and other specific tweaks (e.g. handle TABLE within PRE specially).
+ LMTS formatting is briefly described in the Lynx User Guide, see
+ the section "Lynx and HTML Tables" there. (The Users Guide has not
+ yet been updated for tabular support.)
+
+* TABULAR support for tables
+ Support for tables that really arranges table cells in tabular form.
+
+* Tabular Rendering for SIMPLE Tables (TRST)
+ Tabular support for some tables that are 'simple' enough; what this
+ code change provides.
+
+One basic idea behind providing TRST is that correct tabular support
+for all tables is complex, doesn't fit well into the overwhelmingly
+one-pass way in which Lynx does things, and may in the end not give
+pleasant results anyway for pages that (ab-)use more complex table
+structures for display formatting purposes (especially in view of Lynx
+limitations such as fixed character cell size and lack of horizontal
+scrolling; see also emacs w3 mode). Full table support within Lynx
+hasn't happened so far, and continues to seem unlikely to happen in the
+near future.
+
+The other basic idea is the observation that for simple tables, as
+used mostly for data that are really tabular in nature, LMTS rendering
+can be transformed into TRST rendering, after parsing the TABLE element,
+by two simple transformations applied line by line:
+- Insert spaces in the right places.
+- Shift the line as a whole.
+
+And that's exactly what TRST does. An implementation based on the
+simple observation above is relatively straightforward, for simple
+tables. On encountering the start of a TABLE element, Lynx generates
+output as usual for LMTS. But it also keeps track of cell positions
+and lengths in parallel. If all goes well, that additional information
+is used to fix up the already formatted output lines when the TABLE
+ends. If not all goes well, the table was not 'simple' enough, the
+additional processing is canceled. One advantage is that we always
+have a 'safe' fallback to well-understood traditional LMTS formatting:
+TRST won't make more complex tables look worse than before.
+
+What are 'simple' tables? A table is simple enough if each of its TR
+rows translates into at most one display line in LMTS formatting (excluding
+leading and trailing line breaks), and the width required by each row
+(before as well as after fixup) does not exceed the available screen size.
+Note that this excludes all tables where some of the cells are marked up as
+block elements ('paragraphs'). Tables that include nested TABLE elements
+are always specifically excluded, but the inner tables may be subject to
+TRST handling. Also excluded are some constructs that indicate that markup
+was already optimized for Lynx (or other browsers with no or minimal table
+support): TABLE in PRE, use of TAB.
+
+The description so far isn't completely accurate. In many cases, tables are
+not simple enough according to the last paragraph, but parts of each TR row
+can still benefit from some TRST treatment. Some partial treatment is done
+for some tables in this grey zone, which may or may not help to a better
+display, depending on how the table is used. This is an area where tweaks
+in the future are most expected, and where the code's behavior is currently
+not well defined.
+
+One possible approach:
+- The table is 'simple' according to all criteria set out in the previous
+ paragraph, except that some cells at the beginning and/or end of TR rows
+ may contain block elements (or other markup that results in formatting
+ like separate paragraphs).
+- There is at most one range of (non-empty) table cells in each row whose
+ contents is not paragraph-formatted, and who are rendered on one line
+ together by LMTS, separate from the paragraph-formatted cells. Let's
+ call these cells the 'core' of a row.
+Fixups are then only applied to the text lines showing the 'core' cells.
+The paragraph-formatted cells are effectively pulled out before/after
+their row (no horizontal space is allocated to them for the purpose of
+determining column widths for core line formatting).
+
+This is expected to be most useful for tables that are mostly
+simple tabular data cells, but with the occasional longer
+text thrown in. For example, a table with intended rendering:
+
+ --------------------------------------------------------
+ | date | item no. | price | remarks |
+ |--------|--------------|---------|----------------------|
+ | date-1 | item #1 | $0.00 | |
+ |--------|--------------|---------|----------------------|
+ | date-2 | item #2 | $101.99 | A longer annotation |
+ | | | | marked up as a block |
+ | | | | of text. |
+ |--------|--------------|---------|----------------------|
+ | date-3 | long item #3 | $99.00 | |
+ --------------------------------------------------------
+
+It may now be shown by Lynx as
+
+ .................................................
+
+ date item no. price remarks
+ date-1 item #1 $0.00
+ date-2 item #2 $101.99
+
+ A longer annotation marked up as a block of
+ text.
+
+ date-3 long item #3 $99.00
+
+ .................................................
+
+As can be seen, this is still quite far from the intended rendering,
+but it is better than without any tabular support.
+
+Whether the code does something sensible with "grey area" tables is up
+for testing. Most of the typical tables in typical Web pages aren't
+used in a way that can benefit from the TRST approach. Parts of such
+tables may still end up getting shifted left or right by the TRST code
+when that doesn't improve anything, but I haven't seen it make things
+really worse so far (with the current code).
+
+TRST and Partial Display
+------------------------
+[ Partial display mode is the feature which allows viewing and scrolling
+of pages while they are loaded, without having to wait for a complete
+transfer. ] During partial display rendering, table lines can sometimes
+be shown in the original formatting, i.e. with horizontal fixups not yet
+applied. This is more likely for longer tables, and depends on the state
+in which partial display 'catches' the TRST code. Sometimes the display
+may flicker: first the preliminary rendering of table lines is shown, then
+after loading is finished it is replaced by the fixed-up version. I do
+not consider this a serious problem: if you have partial display mode
+enabled, presumably you want to be able to see as much data as possible,
+and scroll up and down through it, as early as possible. In fact, the
+approach taken keeps Lynx free from a problem that may graphical browsers
+have: they often cannot render a table at all until it is received in full.
+
+------------------------------------------------------------------------
+
+To summarize:
+ - TRST is a solution that works in many cases where lack of tabular support
+ was most annoying.
+ - TRST doesn't implement a full table model, and it is extremely unlikely
+ that it will ever be the basis for that. Keep on exploring external
+ solutions, or perhaps waiting for (better: working on) a more fundamental
+ redesign of Lynx's rendering engine.
+
+Klaus Weide - kweide@enteract.com 1999-10-13