The WebVTT 'line' settings should be parsed as a float

third_party/WebKit/Source/core/html/track/vtt/VTTCue.cpp

 /*
  * Copyright (c) 2013, Opera Software ASA. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 965 matching lines @@
         // Steps 1 - 2 skipped.
         float number;
         // 3. If linepos does not contain at least one ASCII digit, then
         //    jump to the step labeled next setting.
         // 4. If the last character in linepos is a U+0025 PERCENT SIGN
         //    character (%)
         //
         //    If parse a percentage string from linepos doesn't fail, let
         //    number be the returned percentage, otherwise jump to the step
         //    labeled next setting.
-        bool isPercentage = scanPercentage(input, number);
-        if (!isPercentage) {
+        bool isPercentage = input.scanPercentage(number);
+        if (isPercentage) {
+          if (isInvalidPercentage(number))
+            break;
+        } else {
           // Otherwise
           //
           // 1. If linepos contains any characters other than U+002D
-          //    HYPHEN-MINUS characters (-) and ASCII digits, then jump to
-          //    the step labeled next setting.
-          // 2. If any character in linepos other than the first character is
-          //    a U+002D HYPHEN-MINUS character (-), then jump to the step
+          //    HYPHEN-MINUS characters (-), ASCII digits, and U+002E DOT
+          //    character (.), then jump to the step labeled next setting.
+          //
+          // 2. If any character in linepos other than the first character is a
+          //    U+002D HYPHEN-MINUS character (-), then jump to the step
           //    labeled next setting.
+          //
+          // 3. If there are more than one U+002E DOT characters (.), then jump
+          //    to the step labeled next setting.
+          //
+          // 4. If there is a U+002E DOT character (.) and the character before
+          //    or the character after is not an ASCII digit, or if the U+002E
+          //    DOT character (.) is the first or the last character, then jump
+          //    to the step labeled next setting.
+          //
+          // 5. Interpret linepos as a (potentially signed) real number, and

[foolip, 2017/03/03 15:13:57]

Hmm, strictly speaking I guess this is ambiguous for input "-0", and similarly
returning -0 when the input is "0" could be considered correct. Care to file a
spec issue to make this unambiguous?

Also, I don't see any added test, was this already covered?

[fs, 2017/03/03 15:21:03]

Discussed this with the spec editor earlier today =) -
https://github.com/w3c/webvtt/issues/338 - and the current suggestion is to use
HTML's float microsyntax. And that should be consistent with what I've
implemented here.
 
Yes, settings-line.vtt has a cue with a line:-0

[foolip, 2017/03/03 15:25:35]

Yay :)

+          //    let number be that number.
           bool isNegative = input.scan('-');
-          int intLinePosition;
-          if (!input.scanDigits(intLinePosition))
+          if (!input.scanFloat(number))
             break;
-          // 3. Interpret linepos as a (potentially signed) integer, and let
-          //    number be that number.
-          number = isNegative ? -intLinePosition : intLinePosition;
+          // Negate number if it was preceded by a hyphen-minus - unless it's
+          // zero.
+          if (isNegative && number)
+            number = -number;
         }
         if (!input.isAt(valueRun.end()))
           break;
         // 5. Let cue's WebVTT cue line be number.
         m_linePosition = number;
         // 6. If the last character in linepos is a U+0025 PERCENT SIGN
         //    character (%), then let cue's WebVTT cue snap-to-lines
         //    flag be false. Otherwise, let it be true.
         m_snapToLines = !isPercentage;
         // Steps 7 - 9 skipped.
@@ skipping 105 matching lines @@
 
 DEFINE_TRACE(VTTCue) {
   visitor->trace(m_region);
   visitor->trace(m_vttNodeTree);
   visitor->trace(m_cueBackgroundBox);
   visitor->trace(m_displayTree);
   TextTrackCue::trace(visitor);
 }
 
 }  // namespace blink