Bring emphasis up to spec

lib/rules_inline/emphasis.js

@@ -8,12 +8,6 @@ var isPunctChar    = require('../common/utils').isPunctChar;
 var isMdAsciiPunct = require('../common/utils').isMdAsciiPunct;
 
 
-function isAlphaNum(code) {
-  return (code >= 0x30 /* 0 */ && code <= 0x39 /* 9 */) ||
-         (code >= 0x41 /* A */ && code <= 0x5A /* Z */) ||
-         (code >= 0x61 /* a */ && code <= 0x7A /* z */);
-}
-
 // parse sequence of emphasis markers,
 // "start" should point at a valid marker
 function scanDelims(state, start) {
@@ -37,13 +31,15 @@ function scanDelims(state, start) {
     (isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar)));
   isNextPunctChar = nextChar >= 0 &&
     (isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar)));
-  isLastWhiteSpace = lastChar >= 0 && isWhiteSpace(lastChar);
-  isNextWhiteSpace = nextChar >= 0 && isWhiteSpace(nextChar);
+
+  // begin/end of the line counts as a whitespace too
+  isLastWhiteSpace = lastChar < 0 || isWhiteSpace(lastChar);
+  isNextWhiteSpace = nextChar < 0 || isWhiteSpace(nextChar);
 
   if (isNextWhiteSpace) {
     can_open = false;
   } else if (isNextPunctChar) {
-    if (!(isLastWhiteSpace || isLastPunctChar || lastChar === -1)) {
+    if (!(isLastWhiteSpace || isLastPunctChar)) {
       can_open = false;
     }
   }
@@ -51,15 +47,16 @@ function scanDelims(state, start) {
   if (isLastWhiteSpace) {
     can_close = false;
   } else if (isLastPunctChar) {
-    if (!(isNextWhiteSpace || isNextPunctChar || nextChar === -1)) {
+    if (!(isNextWhiteSpace || isNextPunctChar)) {
       can_close = false;
     }
   }
 
   if (marker === 0x5F /* _ */) {
-    // check if we aren't inside the word
-    if (isAlphaNum(lastChar)) { can_open = false; }
-    if (isAlphaNum(nextChar)) { can_close = false; }
+    if (can_open && can_close) {
+      // "_" inside a word can neither open nor close an emphasis
+      can_open = can_close = false;
+    }
   }
 
   return {