Fixed rules for `_`-based emphasis and strong emphasis.

Previously this was not counted as emphasis

    _(bar)_.

because the closing delimiter is both left- and right- flanking.

This fix allows such delimiters, provided they're followed
by punctuation (= they have punctuation on both sides).

Similarly, mutatis mutandis, for opening delimiters and for `__`.

Closes #317.

1 files changed, 58 insertions, 9 deletions

diff --git a/spec.txt b/spec.txt
index c2a867d..f61f5d5 100644
--- a/spec.txt
+++ b/spec.txt
@@ -4643,28 +4643,36 @@ The following rules define emphasis and strong emphasis:
 
 2.  A single `_` character [can open emphasis] iff
     it is part of a [left-flanking delimiter run]
-    and not part of a [right-flanking delimiter run].
+    and either (a) not part of a [right-flanking delimiter run]
+    or (b) part of a [right-flanking delimeter run]
+    preceded by punctuation.
 
 3.  A single `*` character [can close emphasis](@can-close-emphasis)
     iff it is part of a [right-flanking delimiter run].
 
-4.  A single `_` character [can close emphasis]
-    iff it is part of a [right-flanking delimiter run]
-    and not part of a [left-flanking delimiter run].
+4.  A single `_` character [can close emphasis] iff
+    it is part of a [right-flanking delimiter run]
+    and either (a) not part of a [left-flanking delimiter run]
+    or (b) part of a [left-flanking delimeter run]
+    followed by punctuation.
 
 5.  A double `**` [can open strong emphasis](@can-open-strong-emphasis)
     iff it is part of a [left-flanking delimiter run].
 
-6.  A double `__` [can open strong emphasis]
-    iff it is part of a [left-flanking delimiter run]
-    and not part of a [right-flanking delimiter run].
+6.  A double `__` [can open strong emphasis] iff
+    it is part of a [left-flanking delimiter run]
+    and either (a) not part of a [right-flanking delimiter run]
+    or (b) part of a [right-flanking delimeter run]
+    preceded by punctuation.
 
 7.  A double `**` [can close strong emphasis](@can-close-strong-emphasis)
     iff it is part of a [right-flanking delimiter run].
 
 8.  A double `__` [can close strong emphasis]
-    iff it is part of a [right-flanking delimiter run]
-    and not part of a [left-flanking delimiter run].
+    it is part of a [right-flanking delimiter run]
+    and either (a) not part of a [left-flanking delimiter run]
+    or (b) part of a [left-flanking delimeter run]
+    followed by punctuation.
 
 9.  Emphasis begins with a delimiter that [can open emphasis] and ends
     with a delimiter that [can close emphasis], and that uses the same
@@ -4835,6 +4843,16 @@ both left- and right-flanking:
 <p>&quot;aa&quot;_&quot;bb&quot;_&quot;cc&quot;</p>
 .
 
+This is emphasis, even though the opening delimiter is
+both left- and right-flanking, because it is preceded by
+punctuation:
+
+.
+foo-_(bar)
+.
+<p>foo-<em>(bar)</em></p>
+.
+
 Rule 3:
 
 This is not emphasis, because the closing delimiter does
@@ -4943,6 +4961,16 @@ _foo_bar_baz_
 <p><em>foo_bar_baz</em></p>
 .
 
+This is emphasis, even though the closing delimiter is
+both left- and right-flanking, because it is followed by
+punctuation:
+
+.
+_(bar)_.
+.
+<p><em>(bar)</em>.</p>
+.
+
 Rule 5:
 
 .
@@ -5039,6 +5067,17 @@ __foo, __bar__, baz__
 <p><strong>foo, <strong>bar</strong>, baz</strong></p>
 .
 
+This is strong emphasis, even though the opening delimiter is
+both left- and right-flanking, because it is preceded by
+punctuation:
+
+.
+foo-_(bar)_
+.
+<p>foo-<em>(bar)</em></p>
+.
+
+
 Rule 7:
 
 This is not strong emphasis, because the closing delimiter is preceded
@@ -5142,6 +5181,16 @@ __foo__bar__baz__
 <p><strong>foo__bar__baz</strong></p>
 .
 
+This is strong emphasis, even though the closing delimiter is
+both left- and right-flanking, because it is followed by
+punctuation:
+
+.
+_(bar)_.
+.
+<p><em>(bar)</em>.</p>
+.
+
 Rule 9:
 
 Any nonempty sequence of inline elements can be the contents of an