[0.21]

  * Changed handling of tabs.  Instead of having a preprocessing step
    where tabs are converted to spaces, we now handle tabs directly in
    the parser. This allows tabs to be retained in code blocks and code
    spans. This change adds some general language to the effect that,
    for purposes of determining block structure, tabs are to be treated
    just like equivalent spaces.
  * Completely rewrote spec for HTML blocks.  The new spec provides
    better handling of tags like `<del>`, which can be either block
    or inline level content, better handling of custom tags, and
    better handling of verbatim contexts like `<pre>`, comments,
    and `<script>`.
  * Added 9-digit limit on ordered list start number.
    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.
  * Allow (non-initial) hyphens in tag names (#239). Custom
    tags in HTML5 must contain hyphens.
  * Clarified that HTML block is closed at end of containing
    block, not just end of the document (as with fenced code blocks.)
  * Specify nested link definition behavior in prose (Benjamin
    Dumke-von der Ehe).
  * Added test for edge case in link reference parsing
    (Benjamin Dumke-von der Ehe, see jgm/commonmark.js#49).
  * Added link tests with fragment identifiers and queries (David
    Green, #342).
  * Added test cases with a literal backslash in a link destination
    (see jgm/commonmark.js#45).
  * Added test for entity `&ngE;` which resolves to two code points.
    Put entity tests on several lines for readability (see
    jgm/commonmark.js#47).
  * Fixed broken "pre" literal HTML example. Contents
    weren't escaped properly.
  * Simplified defn of "unicode whitespace character,"
    rectifying omission of line tabulation, U+000B (#343).
  * Removed ambiguity in definition of "line" (#346).
  * Rewrapped two prose lines so `+` does not begin a line (#347).
  * Added another test with overlapping emphasis markers.
  * Fixed link to 'attributes'.
  * Revised appendix, "A parsing strategy," and
    added a description of emphasis/link parsing algorithm.
  * `spec_tests.py` - set options for conversions, set library
    paths in a more cross-platform way.
  * `spec_tests.py`: force utf-8 on test failure output and
    `--dump-tests` (#344, #345).
  * `spec_tests.py`: Properly handle visible tab `→` in expected output.
  * `normalize.py`:  Don't collapse whitespace inside pre tag.
  * Added `spec.html` to `.gitignore` (#339).
  * Add `-dev` suffix to spec version after release (eksperimental).
  * Rename "non-space" to "non-whitespace" (Konstantin Zudov, #337).

[0.20]

  * Require at least one nonspace character in a link label (#322).
  * Require replacement (rather than omission) of U+0000 (#327).
  * Clarified that entities resolving to U+0000 are to be
    replaced by U+FFFD (#323).
  * Removed statement that what counts as a line ending is
    platform-dependent (#326).  We now count `\r`, `\n`,
    or `\r\n` as a line ending regardless of the platform.
    (The line ending styles can even be mixed in a single document.)
  * Defined "space."
  * Revised "non-space character". Previously a non-space character
    was defined as anything but a space (U+0020).  Now it is anything
    that is not a whitespace character (as defined in the spec).
  * Clarified that tab expansion is a preprocessing step (#330).
  * Clarified lazy block quote examples (#328).
  * Clarified precedence of indentation that meets conditions for
    both list item continuation blocks and indented code.
  * Added a test case with `#` directly followed by a letter
    (not an ATX header).
  * Added two test cases illustrating that a list at the
    outer level can have items that are indented by more
    than four spaces (see commonmark.js#42 and
    <http://talk.commonmark.org/t/odd-list-behaviour/1189>).
  * Fixed typo in emphasis examples.

[0.19]

  * Fixed rules for `_`-based emphasis and strong emphasis (#317).
    Previously `_(bar)_.` was not parsed as containing emphasis
    because the closing delimiter is both left- and right- flanking.
    This fix allows such delimiters, provided they're followed
    by punctuation (i.e., they have punctuation on both sides).
    Similarly, mutatis mutandis, for opening delimiters and for `__`.
  * Clarified definitions of left-flanking and right-flanking (#310).
    The spec now says explicitly that the beginning and end of line count
    as whitespace for purposes of this definition.
  * Clarified that a code fence followed by header line isn't a header (#306).
  * Fixed alignment in flankingness examples (cosmetic).
  * Fixed last "right flanking but not left flanking" example (#316).
  * Fixed a broken link (Konstantin Zudov).
  * Added link to list of implementations on wiki.
  * Fixed mistake in examples of left/right flanking delimiters
    (Konstantin Zudov).
  * Spell out `iff` (if and only if) the first time it is used (#309).
  * Fixed typos (isoroku, #309).
  * Clarified wording for soft line break: newline can't be preceded
    by two spaces or a backslash.
  * Replaced some references to UTF-8 that should be to unicode.
  * Fixed dingus link in tools/template.html.
  * Replaced obsolete reference to `spec2md.pl` in spec (#304).

[0.18]

  * Added a shortcut link test with mismatched brackets (#282).
  * Added cases with newline whitespace around emphasis open delimiter
    (#282).
  * Added list item examples with no space after marker (#282).
  * Added additional test showing backslash escapes don't work in
    autolinks (#282).
  * Added test for multiline title in reference definition (#282).
  * Added a reference link definition test case (#282).
  * Clarified that link titles can't contain blank lines (#271).
  * Revised Rule 3 for list items (#275).  Previously this just applied to
    empty list items.  It has been rewritten to apply to any list item
    starting with a blank line, including items like:

        -
          ```
          code
          ```

  * Added U+000B and U+000C as whitespace characters (#300).
  * Added comment on sourcepos attribute format in DTD (#298).
  * Use `--smart` option in producing HTML version of spec.
  * Clarified that delimiter runs at beginning/end of line behave as
    if preceded/followed by whitespace (#302).
  * Ensure that URLs in examples have slash after domain.
    This helps with #9, making these tests less sensitive to
    the normalizer used.
  * Fixed typo (Robin Stocker).

[0.17]

  * Improved rule limiting intraword `_` for emphasis and strong emphasis.
    To prevent intra-word emphasis, we used to check to see if
    the delimiter was followed/preceded by an ASCII alphanumeric.
    We now do something more elegant:  whereas an opening `*` must
    be left-flanking, an opening `_` must be left-flanking *and
    not right-flanking*.  And so on for the other cases.
    All the original tests passed except some tests with Russian
    text with internal `_`, which formerly created emphasis but no
    longer do with the new rule.  These tests have been adjusted.
    A few new test cases have been added to illustrate the rule.
  * Added example with link break inside pointy braces (no link) (#295).
  * Added spec example: loose list with blank line after fenced code (#285).

[0.16]

  * Rewrote beginning of Entities section, clarifying that only
    entities not in code blocks or spans are decoded.
  * Removed defective Example 449 (#284).
  * Fixed typo (#283).
  * Added intended two-space hard-breaks in Examples 521, 523.
  * Clarified that brackets in general don't take precedence over emph
    (#258).
  * Clarified that final newline is removed from paragraph content
    (#176).
  * Talk of "info string" rather than "attributes" for code blocks
    (#262).
  * Clarified precedence of code spans, HTML tags, autolinks (#259).
  * Fixed a number of internal links and duplicate references in the spec.
  * Linkify "info string" in spec.
  * Use shortcut reference links when possible in spec.txt.
  * cmark itself is now used to build spec.html, rather than pandoc.
  * Use shortcut reference links when possible in spec.txt. This
    relies on the new `spec2md.py` behavior of creating references
    for all internal anchors.
  * Moved some examples from block to inline HTML section.
  * Added examples of non-comments (#264).
  * Changed rule for comments to conform to HTML5 spec.
  * Made clear that any sequence of characters is a valid document
    (#266).
  * Changed wording: "is preferred" -> "takes precedence."
  * Regularized spelling of "non-space character" and added links
    (#260).
  * Use four spaces rather than five to show "four spaces is too much"
    (#261).

[0.15]

  * Fixed some typos with "left-" and "right-flanking" delimiters in the
    section on emphasis and strong emphasis (#257).

[0.14]

  * Clarified indented code blocks. Previously the spec said, wrongly,
    that a blank line was needed between a paragraph and a following
    code block.  It is only needed between a code block and a following
    paragraph (due to lazy continuations). (Thanks to textnut.)
  * Added definitions of whitespace, unicode whitespace, punctuation,
    ASCII punctuation (#108).
  * Improved rules for emphasis and strong emphasis. This improves
    parsing of emphasis around punctuation. For background see
    <http://talk.commonmark.org/t/903/6>. The basic idea of the change
    is that if the delimiter is part of a delimiter clump that has
    punctuation to the left and a normal character (non-space,
    non-punctuation) to the right, it can only be an opener.  If it has
    punctuation to the right and a normal character (non-space,
    non-punctuation) to the left, it can only be a closer. This handles
    cases like

          **Gomphocarpus (*Gomphocarpus physocarpus*, syn. *Asclepias
          physocarpa*)**

    and

          **foo "*bar*" foo**

    better than before.
  * Added test case for link-in-link-in-image (#252).
  * Fixed broken internal references.
  * Added another example of an unclarity in the canonical Markdown
    syntax description.
  * Reworded the principle of uniformity to be more general; it applies
    to all container blocks, not just list items.
  * Added a rule for empty list items (#242).
  * Clarified precedence of empty list items over setext header lines
    (#95).
  * Added an example with two blank lines in fenced code in a sublist (#180).
  * Added an explicit CC-BY-SA license to the spec (#55).

[0.13]

  * Updated path of test program.
  * Use terminology "plain textual content" instead of "string."
  * Added condition that conforming parsers strip or replace NULL characters.
  * Changed Example 196 to reflect the spec's rules.  It should not be a loose
    list as it has no blank lines.
  * Adjusted semantically insignificant formatting of HTML output.
  * Added example to spec of shortcut link with following space (#214).