Added 9-digit limit on ordered list start number.

Intent is to avoid problems with overflows.

See
http://talk.commonmark.org/t/what-is-or-what-should-be-the-range-of-indices-of-ordered-list-items/1249

Some browsers use signed 32-bit integers for indexing
the items of an ordered list, and this can lead to odd
or undefined behavior if 10-digit start numbers are allowed.

1 files changed, 47 insertions, 2 deletions

diff --git a/spec.txt b/spec.txt
index 9b5e9dc..4062998 100644
--- a/spec.txt
+++ b/spec.txt
@@ -3104,8 +3104,10 @@ A [bullet list marker](@bullet-list-marker)
 is a `-`, `+`, or `*` character.
 
 An [ordered list marker](@ordered-list-marker)
-is a sequence of one of more digits (`0-9`), followed by either a
-`.` character or a `)` character.
+is a sequence of 1--9 arabic digits (`0-9`), followed by either a
+`.` character or a `)` character.  (The reason for the length
+limit is that with 10 digits we start seeing integer overflows
+in some browsers.)
 
 The following rules define [list items]:
 
@@ -3374,6 +3376,49 @@ A list item may contain any kind of block:
 </ol>
 .
 
+Note that ordered list start numbers must be nine digits or less:
+
+.
+123456789. ok
+.
+<ol start="123456789">
+<li>ok</li>
+</ol>
+.
+
+.
+1234567890. not ok
+.
+<p>1234567890. not ok</p>
+.
+
+A start number may begin with 0s:
+
+.
+0. ok
+.
+<ol start="0">
+<li>ok</li>
+</ol>
+.
+
+.
+003. ok
+.
+<ol start="3">
+<li>ok</li>
+</ol>
+.
+
+A start number may not be negative:
+
+.
+-1. not ok
+.
+<p>-1. not ok</p>
+.
+
+
 2.  **Item starting with indented code.**  If a sequence of lines *Ls*
     constitute a sequence of blocks *Bs* starting with an indented code
     block and not separated from each other by more than one blank line,