ConTeXt writer: Use xtables instead of Tables (#4223)

- Default to xtables for context output.
- Added `ntb` extension (affecting context writer only) to use Natural Tables instead.
- Added `Ext_ntb` constructor to `Extension` (API change).

1 files changed, 210 insertions, 155 deletions

diff --git a/test/tables.context b/test/tables.context
index 371e559e5..89ff4a025 100644
--- a/test/tables.context
+++ b/test/tables.context
@@ -1,175 +1,230 @@
 Simple table with caption:
 
-\placetable{Demonstration of simple table syntax.}
-\starttable[|r|l|c|l|]
-\HL
-\NC Right
-\NC Left
-\NC Center
-\NC Default
-\NC\AR
-\HL
-\NC 12
-\NC 12
-\NC 12
-\NC 12
-\NC\AR
-\NC 123
-\NC 123
-\NC 123
-\NC 123
-\NC\AR
-\NC 1
-\NC 1
-\NC 1
-\NC 1
-\NC\AR
-\HL
-\stoptable
+\startplacetable[caption={Demonstration of simple table syntax.}]
+\startxtable
+\startxtablehead[head]
+\startxrow
+\startxcell[align=left] Right \stopxcell
+\startxcell[align=right] Left \stopxcell
+\startxcell[align=middle] Center \stopxcell
+\startxcell Default \stopxcell
+\stopxrow
+\stopxtablehead
+\startxtablebody[body]
+\startxrow
+\startxcell[align=left] 12 \stopxcell
+\startxcell[align=right] 12 \stopxcell
+\startxcell[align=middle] 12 \stopxcell
+\startxcell 12 \stopxcell
+\stopxrow
+\startxrow
+\startxcell[align=left] 123 \stopxcell
+\startxcell[align=right] 123 \stopxcell
+\startxcell[align=middle] 123 \stopxcell
+\startxcell 123 \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=left] 1 \stopxcell
+\startxcell[align=right] 1 \stopxcell
+\startxcell[align=middle] 1 \stopxcell
+\startxcell 1 \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Simple table without caption:
 
-\placetable[none]{}
-\starttable[|r|l|c|l|]
-\HL
-\NC Right
-\NC Left
-\NC Center
-\NC Default
-\NC\AR
-\HL
-\NC 12
-\NC 12
-\NC 12
-\NC 12
-\NC\AR
-\NC 123
-\NC 123
-\NC 123
-\NC 123
-\NC\AR
-\NC 1
-\NC 1
-\NC 1
-\NC 1
-\NC\AR
-\HL
-\stoptable
+\startplacetable[location=none]
+\startxtable
+\startxtablehead[head]
+\startxrow
+\startxcell[align=left] Right \stopxcell
+\startxcell[align=right] Left \stopxcell
+\startxcell[align=middle] Center \stopxcell
+\startxcell Default \stopxcell
+\stopxrow
+\stopxtablehead
+\startxtablebody[body]
+\startxrow
+\startxcell[align=left] 12 \stopxcell
+\startxcell[align=right] 12 \stopxcell
+\startxcell[align=middle] 12 \stopxcell
+\startxcell 12 \stopxcell
+\stopxrow
+\startxrow
+\startxcell[align=left] 123 \stopxcell
+\startxcell[align=right] 123 \stopxcell
+\startxcell[align=middle] 123 \stopxcell
+\startxcell 123 \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=left] 1 \stopxcell
+\startxcell[align=right] 1 \stopxcell
+\startxcell[align=middle] 1 \stopxcell
+\startxcell 1 \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Simple table indented two spaces:
 
-\placetable{Demonstration of simple table syntax.}
-\starttable[|r|l|c|l|]
-\HL
-\NC Right
-\NC Left
-\NC Center
-\NC Default
-\NC\AR
-\HL
-\NC 12
-\NC 12
-\NC 12
-\NC 12
-\NC\AR
-\NC 123
-\NC 123
-\NC 123
-\NC 123
-\NC\AR
-\NC 1
-\NC 1
-\NC 1
-\NC 1
-\NC\AR
-\HL
-\stoptable
+\startplacetable[caption={Demonstration of simple table syntax.}]
+\startxtable
+\startxtablehead[head]
+\startxrow
+\startxcell[align=left] Right \stopxcell
+\startxcell[align=right] Left \stopxcell
+\startxcell[align=middle] Center \stopxcell
+\startxcell Default \stopxcell
+\stopxrow
+\stopxtablehead
+\startxtablebody[body]
+\startxrow
+\startxcell[align=left] 12 \stopxcell
+\startxcell[align=right] 12 \stopxcell
+\startxcell[align=middle] 12 \stopxcell
+\startxcell 12 \stopxcell
+\stopxrow
+\startxrow
+\startxcell[align=left] 123 \stopxcell
+\startxcell[align=right] 123 \stopxcell
+\startxcell[align=middle] 123 \stopxcell
+\startxcell 123 \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=left] 1 \stopxcell
+\startxcell[align=right] 1 \stopxcell
+\startxcell[align=middle] 1 \stopxcell
+\startxcell 1 \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Multiline table with caption:
 
-\placetable{Here's the caption. It may span multiple lines.}
-\starttable[|cp(0.15\textwidth)|lp(0.14\textwidth)|rp(0.16\textwidth)|lp(0.34\textwidth)|]
-\HL
-\NC Centered Header
-\NC Left Aligned
-\NC Right Aligned
-\NC Default aligned
-\NC\AR
-\HL
-\NC First
-\NC row
-\NC 12.0
-\NC Example of a row that spans multiple lines.
-\NC\AR
-\NC Second
-\NC row
-\NC 5.0
-\NC Here's another one. Note the blank line between rows.
-\NC\AR
-\HL
-\stoptable
+\startplacetable[caption={Here's the caption. It may span multiple lines.}]
+\startxtable
+\startxtablehead[head]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] Centered Header \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] Left Aligned \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] Right Aligned \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Default aligned \stopxcell
+\stopxrow
+\stopxtablehead
+\startxtablebody[body]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] First \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 12.0 \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Example of a row that spans
+multiple lines. \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] Second \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 5.0 \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Here's another one. Note the
+blank line between rows. \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Multiline table without caption:
 
-\placetable[none]{}
-\starttable[|cp(0.15\textwidth)|lp(0.14\textwidth)|rp(0.16\textwidth)|lp(0.34\textwidth)|]
-\HL
-\NC Centered Header
-\NC Left Aligned
-\NC Right Aligned
-\NC Default aligned
-\NC\AR
-\HL
-\NC First
-\NC row
-\NC 12.0
-\NC Example of a row that spans multiple lines.
-\NC\AR
-\NC Second
-\NC row
-\NC 5.0
-\NC Here's another one. Note the blank line between rows.
-\NC\AR
-\HL
-\stoptable
+\startplacetable[location=none]
+\startxtable
+\startxtablehead[head]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] Centered Header \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] Left Aligned \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] Right Aligned \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Default aligned \stopxcell
+\stopxrow
+\stopxtablehead
+\startxtablebody[body]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] First \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 12.0 \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Example of a row that spans
+multiple lines. \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] Second \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 5.0 \stopxcell
+\startxcell[align=right,width={0.34\textwidth}] Here's another one. Note the
+blank line between rows. \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Table without column headers:
 
-\placetable[none]{}
-\starttable[|r|l|c|r|]
-\HL
-\NC 12
-\NC 12
-\NC 12
-\NC 12
-\NC\AR
-\NC 123
-\NC 123
-\NC 123
-\NC 123
-\NC\AR
-\NC 1
-\NC 1
-\NC 1
-\NC 1
-\NC\AR
-\HL
-\stoptable
+\startplacetable[location=none]
+\startxtable
+\startxtablebody[body]
+\startxrow
+\startxcell[align=left] 12 \stopxcell
+\startxcell[align=right] 12 \stopxcell
+\startxcell[align=middle] 12 \stopxcell
+\startxcell[align=left] 12 \stopxcell
+\stopxrow
+\startxrow
+\startxcell[align=left] 123 \stopxcell
+\startxcell[align=right] 123 \stopxcell
+\startxcell[align=middle] 123 \stopxcell
+\startxcell[align=left] 123 \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=left] 1 \stopxcell
+\startxcell[align=right] 1 \stopxcell
+\startxcell[align=middle] 1 \stopxcell
+\startxcell[align=left] 1 \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable
 
 Multiline table without column headers:
 
-\placetable[none]{}
-\starttable[|cp(0.15\textwidth)|lp(0.14\textwidth)|rp(0.16\textwidth)|lp(0.34\textwidth)|]
-\HL
-\NC First
-\NC row
-\NC 12.0
-\NC Example of a row that spans multiple lines.
-\NC\AR
-\NC Second
-\NC row
-\NC 5.0
-\NC Here's another one. Note the blank line between rows.
-\NC\AR
-\HL
-\stoptable
+\startplacetable[location=none]
+\startxtable
+\startxtablebody[body]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] First \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 12.0 \stopxcell
+\startxcell[width={0.34\textwidth}] Example of a row that spans multiple
+lines. \stopxcell
+\stopxrow
+\stopxtablebody
+\startxtablefoot[foot]
+\startxrow
+\startxcell[align=middle,width={0.15\textwidth}] Second \stopxcell
+\startxcell[align=right,width={0.14\textwidth}] row \stopxcell
+\startxcell[align=left,width={0.16\textwidth}] 5.0 \stopxcell
+\startxcell[width={0.34\textwidth}] Here's another one. Note the blank line
+between rows. \stopxcell
+\stopxrow
+\stopxtablefoot
+\stopxtable
+\stopplacetable