Update Blackfriday dependency (closes #522) (#532)

- Fixup Telegram bridge implementation to support updated dependency.

1 files changed, 385 insertions, 376 deletions

diff --git a/vendor/github.com/russross/blackfriday/markdown.go b/vendor/github.com/russross/blackfriday/markdown.go
index 1722a738..ff61cb05 100644
--- a/vendor/github.com/russross/blackfriday/markdown.go
+++ b/vendor/github.com/russross/blackfriday/markdown.go
@@ -1,230 +1,200 @@
-//
 // Blackfriday Markdown Processor
 // Available at http://github.com/russross/blackfriday
 //
 // Copyright © 2011 Russ Ross <russ@russross.com>.
 // Distributed under the Simplified BSD License.
 // See README.md for details.
-//
-
-//
-//
-// Markdown parsing and processing
-//
-//
 
 package blackfriday
 
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"strings"
 	"unicode/utf8"
 )
 
-const VERSION = "1.5"
+//
+// Markdown parsing and processing
+//
+
+// Version string of the package. Appears in the rendered document when
+// CompletePage flag is on.
+const Version = "2.0"
+
+// Extensions is a bitwise or'ed collection of enabled Blackfriday's
+// extensions.
+type Extensions int
 
 // These are the supported markdown parsing extensions.
 // OR these values together to select multiple extensions.
 const (
-	EXTENSION_NO_INTRA_EMPHASIS          = 1 << iota // ignore emphasis markers inside words
-	EXTENSION_TABLES                                 // render tables
-	EXTENSION_FENCED_CODE                            // render fenced code blocks
-	EXTENSION_AUTOLINK                               // detect embedded URLs that are not explicitly marked
-	EXTENSION_STRIKETHROUGH                          // strikethrough text using ~~test~~
-	EXTENSION_LAX_HTML_BLOCKS                        // loosen up HTML block parsing rules
-	EXTENSION_SPACE_HEADERS                          // be strict about prefix header rules
-	EXTENSION_HARD_LINE_BREAK                        // translate newlines into line breaks
-	EXTENSION_TAB_SIZE_EIGHT                         // expand tabs to eight spaces instead of four
-	EXTENSION_FOOTNOTES                              // Pandoc-style footnotes
-	EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK             // No need to insert an empty line to start a (code, quote, ordered list, unordered list) block
-	EXTENSION_HEADER_IDS                             // specify header IDs  with {#id}
-	EXTENSION_TITLEBLOCK                             // Titleblock ala pandoc
-	EXTENSION_AUTO_HEADER_IDS                        // Create the header ID from the text
-	EXTENSION_BACKSLASH_LINE_BREAK                   // translate trailing backslashes into line breaks
-	EXTENSION_DEFINITION_LISTS                       // render definition lists
-	EXTENSION_JOIN_LINES                             // delete newline and join lines
-
-	commonHtmlFlags = 0 |
-		HTML_USE_XHTML |
-		HTML_USE_SMARTYPANTS |
-		HTML_SMARTYPANTS_FRACTIONS |
-		HTML_SMARTYPANTS_DASHES |
-		HTML_SMARTYPANTS_LATEX_DASHES
-
-	commonExtensions = 0 |
-		EXTENSION_NO_INTRA_EMPHASIS |
-		EXTENSION_TABLES |
-		EXTENSION_FENCED_CODE |
-		EXTENSION_AUTOLINK |
-		EXTENSION_STRIKETHROUGH |
-		EXTENSION_SPACE_HEADERS |
-		EXTENSION_HEADER_IDS |
-		EXTENSION_BACKSLASH_LINE_BREAK |
-		EXTENSION_DEFINITION_LISTS
+	NoExtensions           Extensions = 0
+	NoIntraEmphasis        Extensions = 1 << iota // Ignore emphasis markers inside words
+	Tables                                        // Render tables
+	FencedCode                                    // Render fenced code blocks
+	Autolink                                      // Detect embedded URLs that are not explicitly marked
+	Strikethrough                                 // Strikethrough text using ~~test~~
+	LaxHTMLBlocks                                 // Loosen up HTML block parsing rules
+	SpaceHeadings                                 // Be strict about prefix heading rules
+	HardLineBreak                                 // Translate newlines into line breaks
+	TabSizeEight                                  // Expand tabs to eight spaces instead of four
+	Footnotes                                     // Pandoc-style footnotes
+	NoEmptyLineBeforeBlock                        // No need to insert an empty line to start a (code, quote, ordered list, unordered list) block
+	HeadingIDs                                    // specify heading IDs  with {#id}
+	Titleblock                                    // Titleblock ala pandoc
+	AutoHeadingIDs                                // Create the heading ID from the text
+	BackslashLineBreak                            // Translate trailing backslashes into line breaks
+	DefinitionLists                               // Render definition lists
+
+	CommonHTMLFlags HTMLFlags = UseXHTML | Smartypants |
+		SmartypantsFractions | SmartypantsDashes | SmartypantsLatexDashes
+
+	CommonExtensions Extensions = NoIntraEmphasis | Tables | FencedCode |
+		Autolink | Strikethrough | SpaceHeadings | HeadingIDs |
+		BackslashLineBreak | DefinitionLists
 )
 
-// These are the possible flag values for the link renderer.
-// Only a single one of these values will be used; they are not ORed together.
-// These are mostly of interest if you are writing a new output format.
-const (
-	LINK_TYPE_NOT_AUTOLINK = iota
-	LINK_TYPE_NORMAL
-	LINK_TYPE_EMAIL
-)
+// ListType contains bitwise or'ed flags for list and list item objects.
+type ListType int
 
 // These are the possible flag values for the ListItem renderer.
 // Multiple flag values may be ORed together.
 // These are mostly of interest if you are writing a new output format.
 const (
-	LIST_TYPE_ORDERED = 1 << iota
-	LIST_TYPE_DEFINITION
-	LIST_TYPE_TERM
-	LIST_ITEM_CONTAINS_BLOCK
-	LIST_ITEM_BEGINNING_OF_LIST
-	LIST_ITEM_END_OF_LIST
+	ListTypeOrdered ListType = 1 << iota
+	ListTypeDefinition
+	ListTypeTerm
+
+	ListItemContainsBlock
+	ListItemBeginningOfList // TODO: figure out if this is of any use now
+	ListItemEndOfList
 )
 
+// CellAlignFlags holds a type of alignment in a table cell.
+type CellAlignFlags int
+
 // These are the possible flag values for the table cell renderer.
 // Only a single one of these values will be used; they are not ORed together.
 // These are mostly of interest if you are writing a new output format.
 const (
-	TABLE_ALIGNMENT_LEFT = 1 << iota
-	TABLE_ALIGNMENT_RIGHT
-	TABLE_ALIGNMENT_CENTER = (TABLE_ALIGNMENT_LEFT | TABLE_ALIGNMENT_RIGHT)
+	TableAlignmentLeft CellAlignFlags = 1 << iota
+	TableAlignmentRight
+	TableAlignmentCenter = (TableAlignmentLeft | TableAlignmentRight)
 )
 
 // The size of a tab stop.
 const (
-	TAB_SIZE_DEFAULT = 4
-	TAB_SIZE_EIGHT   = 8
+	TabSizeDefault = 4
+	TabSizeDouble  = 8
 )
 
 // blockTags is a set of tags that are recognized as HTML block tags.
 // Any of these can be included in markdown text without special escaping.
 var blockTags = map[string]struct{}{
-	"blockquote": {},
-	"del":        {},
-	"div":        {},
-	"dl":         {},
-	"fieldset":   {},
-	"form":       {},
-	"h1":         {},
-	"h2":         {},
-	"h3":         {},
-	"h4":         {},
-	"h5":         {},
-	"h6":         {},
-	"iframe":     {},
-	"ins":        {},
-	"math":       {},
-	"noscript":   {},
-	"ol":         {},
-	"pre":        {},
-	"p":          {},
-	"script":     {},
-	"style":      {},
-	"table":      {},
-	"ul":         {},
+	"blockquote": struct{}{},
+	"del":        struct{}{},
+	"div":        struct{}{},
+	"dl":         struct{}{},
+	"fieldset":   struct{}{},
+	"form":       struct{}{},
+	"h1":         struct{}{},
+	"h2":         struct{}{},
+	"h3":         struct{}{},
+	"h4":         struct{}{},
+	"h5":         struct{}{},
+	"h6":         struct{}{},
+	"iframe":     struct{}{},
+	"ins":        struct{}{},
+	"math":       struct{}{},
+	"noscript":   struct{}{},
+	"ol":         struct{}{},
+	"pre":        struct{}{},
+	"p":          struct{}{},
+	"script":     struct{}{},
+	"style":      struct{}{},
+	"table":      struct{}{},
+	"ul":         struct{}{},
 
 	// HTML5
-	"address":    {},
-	"article":    {},
-	"aside":      {},
-	"canvas":     {},
-	"figcaption": {},
-	"figure":     {},
-	"footer":     {},
-	"header":     {},
-	"hgroup":     {},
-	"main":       {},
-	"nav":        {},
-	"output":     {},
-	"progress":   {},
-	"section":    {},
-	"video":      {},
+	"address":    struct{}{},
+	"article":    struct{}{},
+	"aside":      struct{}{},
+	"canvas":     struct{}{},
+	"figcaption": struct{}{},
+	"figure":     struct{}{},
+	"footer":     struct{}{},
+	"header":     struct{}{},
+	"hgroup":     struct{}{},
+	"main":       struct{}{},
+	"nav":        struct{}{},
+	"output":     struct{}{},
+	"progress":   struct{}{},
+	"section":    struct{}{},
+	"video":      struct{}{},
 }
 
-// Renderer is the rendering interface.
-// This is mostly of interest if you are implementing a new rendering format.
+// Renderer is the rendering interface. This is mostly of interest if you are
+// implementing a new rendering format.
 //
-// When a byte slice is provided, it contains the (rendered) contents of the
-// element.
-//
-// When a callback is provided instead, it will write the contents of the
-// respective element directly to the output buffer and return true on success.
-// If the callback returns false, the rendering function should reset the
-// output buffer as though it had never been called.
-//
-// Currently Html and Latex implementations are provided
+// Only an HTML implementation is provided in this repository, see the README
+// for external implementations.
 type Renderer interface {
-	// block-level callbacks
-	BlockCode(out *bytes.Buffer, text []byte, lang string)
-	BlockQuote(out *bytes.Buffer, text []byte)
-	BlockHtml(out *bytes.Buffer, text []byte)
-	Header(out *bytes.Buffer, text func() bool, level int, id string)
-	HRule(out *bytes.Buffer)
-	List(out *bytes.Buffer, text func() bool, flags int)
-	ListItem(out *bytes.Buffer, text []byte, flags int)
-	Paragraph(out *bytes.Buffer, text func() bool)
-	Table(out *bytes.Buffer, header []byte, body []byte, columnData []int)
-	TableRow(out *bytes.Buffer, text []byte)
-	TableHeaderCell(out *bytes.Buffer, text []byte, flags int)
-	TableCell(out *bytes.Buffer, text []byte, flags int)
-	Footnotes(out *bytes.Buffer, text func() bool)
-	FootnoteItem(out *bytes.Buffer, name, text []byte, flags int)
-	TitleBlock(out *bytes.Buffer, text []byte)
-
-	// Span-level callbacks
-	AutoLink(out *bytes.Buffer, link []byte, kind int)
-	CodeSpan(out *bytes.Buffer, text []byte)
-	DoubleEmphasis(out *bytes.Buffer, text []byte)
-	Emphasis(out *bytes.Buffer, text []byte)
-	Image(out *bytes.Buffer, link []byte, title []byte, alt []byte)
-	LineBreak(out *bytes.Buffer)
-	Link(out *bytes.Buffer, link []byte, title []byte, content []byte)
-	RawHtmlTag(out *bytes.Buffer, tag []byte)
-	TripleEmphasis(out *bytes.Buffer, text []byte)
-	StrikeThrough(out *bytes.Buffer, text []byte)
-	FootnoteRef(out *bytes.Buffer, ref []byte, id int)
-
-	// Low-level callbacks
-	Entity(out *bytes.Buffer, entity []byte)
-	NormalText(out *bytes.Buffer, text []byte)
-
-	// Header and footer
-	DocumentHeader(out *bytes.Buffer)
-	DocumentFooter(out *bytes.Buffer)
-
-	GetFlags() int
+	// RenderNode is the main rendering method. It will be called once for
+	// every leaf node and twice for every non-leaf node (first with
+	// entering=true, then with entering=false). The method should write its
+	// rendition of the node to the supplied writer w.
+	RenderNode(w io.Writer, node *Node, entering bool) WalkStatus
+
+	// RenderHeader is a method that allows the renderer to produce some
+	// content preceding the main body of the output document. The header is
+	// understood in the broad sense here. For example, the default HTML
+	// renderer will write not only the HTML document preamble, but also the
+	// table of contents if it was requested.
+	//
+	// The method will be passed an entire document tree, in case a particular
+	// implementation needs to inspect it to produce output.
+	//
+	// The output should be written to the supplied writer w. If your
+	// implementation has no header to write, supply an empty implementation.
+	RenderHeader(w io.Writer, ast *Node)
+
+	// RenderFooter is a symmetric counterpart of RenderHeader.
+	RenderFooter(w io.Writer, ast *Node)
 }
 
 // Callback functions for inline parsing. One such function is defined
 // for each character that triggers a response when parsing inline data.
-type inlineParser func(p *parser, out *bytes.Buffer, data []byte, offset int) int
-
-// Parser holds runtime state used by the parser.
-// This is constructed by the Markdown function.
-type parser struct {
-	r              Renderer
-	refOverride    ReferenceOverrideFunc
-	refs           map[string]*reference
-	inlineCallback [256]inlineParser
-	flags          int
-	nesting        int
-	maxNesting     int
-	insideLink     bool
+type inlineParser func(p *Markdown, data []byte, offset int) (int, *Node)
+
+// Markdown is a type that holds extensions and the runtime state used by
+// Parse, and the renderer. You can not use it directly, construct it with New.
+type Markdown struct {
+	renderer          Renderer
+	referenceOverride ReferenceOverrideFunc
+	refs              map[string]*reference
+	inlineCallback    [256]inlineParser
+	extensions        Extensions
+	nesting           int
+	maxNesting        int
+	insideLink        bool
 
 	// Footnotes need to be ordered as well as available to quickly check for
 	// presence. If a ref is also a footnote, it's stored both in refs and here
 	// in notes. Slice is nil if footnotes not enabled.
-	notes       []*reference
-	notesRecord map[string]struct{}
+	notes []*reference
+
+	doc                  *Node
+	tip                  *Node // = doc
+	oldTip               *Node
+	lastMatchedContainer *Node // = doc
+	allClosed            bool
 }
 
-func (p *parser) getRef(refid string) (ref *reference, found bool) {
-	if p.refOverride != nil {
-		r, overridden := p.refOverride(refid)
+func (p *Markdown) getRef(refid string) (ref *reference, found bool) {
+	if p.referenceOverride != nil {
+		r, overridden := p.referenceOverride(refid)
 		if overridden {
 			if r == nil {
 				return nil, false
@@ -232,7 +202,7 @@ func (p *parser) getRef(refid string) (ref *reference, found bool) {
 			return &reference{
 				link:     []byte(r.Link),
 				title:    []byte(r.Title),
-				noteId:   0,
+				noteID:   0,
 				hasBlock: false,
 				text:     []byte(r.Text)}, true
 		}
@@ -242,9 +212,34 @@ func (p *parser) getRef(refid string) (ref *reference, found bool) {
 	return ref, found
 }
 
-func (p *parser) isFootnote(ref *reference) bool {
-	_, ok := p.notesRecord[string(ref.link)]
-	return ok
+func (p *Markdown) finalize(block *Node) {
+	above := block.Parent
+	block.open = false
+	p.tip = above
+}
+
+func (p *Markdown) addChild(node NodeType, offset uint32) *Node {
+	return p.addExistingChild(NewNode(node), offset)
+}
+
+func (p *Markdown) addExistingChild(node *Node, offset uint32) *Node {
+	for !p.tip.canContain(node.Type) {
+		p.finalize(p.tip)
+	}
+	p.tip.AppendChild(node)
+	p.tip = node
+	return node
+}
+
+func (p *Markdown) closeUnmatchedBlocks() {
+	if !p.allClosed {
+		for p.oldTip != p.lastMatchedContainer {
+			parent := p.oldTip.Parent
+			p.finalize(p.oldTip)
+			p.oldTip = parent
+		}
+		p.allClosed = true
+	}
 }
 
 //
@@ -271,102 +266,27 @@ type Reference struct {
 // See the documentation in Options for more details on use-case.
 type ReferenceOverrideFunc func(reference string) (ref *Reference, overridden bool)
 
-// Options represents configurable overrides and callbacks (in addition to the
-// extension flag set) for configuring a Markdown parse.
-type Options struct {
-	// Extensions is a flag set of bit-wise ORed extension bits. See the
-	// EXTENSION_* flags defined in this package.
-	Extensions int
-
-	// ReferenceOverride is an optional function callback that is called every
-	// time a reference is resolved.
-	//
-	// In Markdown, the link reference syntax can be made to resolve a link to
-	// a reference instead of an inline URL, in one of the following ways:
-	//
-	//  * [link text][refid]
-	//  * [refid][]
-	//
-	// Usually, the refid is defined at the bottom of the Markdown document. If
-	// this override function is provided, the refid is passed to the override
-	// function first, before consulting the defined refids at the bottom. If
-	// the override function indicates an override did not occur, the refids at
-	// the bottom will be used to fill in the link details.
-	ReferenceOverride ReferenceOverrideFunc
-}
-
-// MarkdownBasic is a convenience function for simple rendering.
-// It processes markdown input with no extensions enabled.
-func MarkdownBasic(input []byte) []byte {
-	// set up the HTML renderer
-	htmlFlags := HTML_USE_XHTML
-	renderer := HtmlRenderer(htmlFlags, "", "")
-
-	// set up the parser
-	return MarkdownOptions(input, renderer, Options{Extensions: 0})
-}
-
-// Call Markdown with most useful extensions enabled
-// MarkdownCommon is a convenience function for simple rendering.
-// It processes markdown input with common extensions enabled, including:
-//
-// * Smartypants processing with smart fractions and LaTeX dashes
-//
-// * Intra-word emphasis suppression
-//
-// * Tables
-//
-// * Fenced code blocks
-//
-// * Autolinking
-//
-// * Strikethrough support
-//
-// * Strict header parsing
-//
-// * Custom Header IDs
-func MarkdownCommon(input []byte) []byte {
-	// set up the HTML renderer
-	renderer := HtmlRenderer(commonHtmlFlags, "", "")
-	return MarkdownOptions(input, renderer, Options{
-		Extensions: commonExtensions})
-}
-
-// Markdown is the main rendering function.
-// It parses and renders a block of markdown-encoded text.
-// The supplied Renderer is used to format the output, and extensions dictates
-// which non-standard extensions are enabled.
-//
-// To use the supplied Html or LaTeX renderers, see HtmlRenderer and
-// LatexRenderer, respectively.
-func Markdown(input []byte, renderer Renderer, extensions int) []byte {
-	return MarkdownOptions(input, renderer, Options{
-		Extensions: extensions})
-}
-
-// MarkdownOptions is just like Markdown but takes additional options through
-// the Options struct.
-func MarkdownOptions(input []byte, renderer Renderer, opts Options) []byte {
-	// no point in parsing if we can't render
-	if renderer == nil {
-		return nil
+// New constructs a Markdown processor. You can use the same With* functions as
+// for Run() to customize parser's behavior and the renderer.
+func New(opts ...Option) *Markdown {
+	var p Markdown
+	for _, opt := range opts {
+		opt(&p)
 	}
-
-	extensions := opts.Extensions
-
-	// fill in the render structure
-	p := new(parser)
-	p.r = renderer
-	p.flags = extensions
-	p.refOverride = opts.ReferenceOverride
 	p.refs = make(map[string]*reference)
 	p.maxNesting = 16
 	p.insideLink = false
-
+	docNode := NewNode(Document)
+	p.doc = docNode
+	p.tip = docNode
+	p.oldTip = docNode
+	p.lastMatchedContainer = docNode
+	p.allClosed = true
 	// register inline parsers
+	p.inlineCallback[' '] = maybeLineBreak
 	p.inlineCallback['*'] = emphasis
 	p.inlineCallback['_'] = emphasis
-	if extensions&EXTENSION_STRIKETHROUGH != 0 {
+	if p.extensions&Strikethrough != 0 {
 		p.inlineCallback['~'] = emphasis
 	}
 	p.inlineCallback['`'] = codeSpan
@@ -375,116 +295,166 @@ func MarkdownOptions(input []byte, renderer Renderer, opts Options) []byte {
 	p.inlineCallback['<'] = leftAngle
 	p.inlineCallback['\\'] = escape
 	p.inlineCallback['&'] = entity
-
-	if extensions&EXTENSION_AUTOLINK != 0 {
-		p.inlineCallback[':'] = autoLink
-	}
-
-	if extensions&EXTENSION_FOOTNOTES != 0 {
+	p.inlineCallback['!'] = maybeImage
+	p.inlineCallback['^'] = maybeInlineFootnote
+	if p.extensions&Autolink != 0 {
+		p.inlineCallback['h'] = maybeAutoLink
+		p.inlineCallback['m'] = maybeAutoLink
+		p.inlineCallback['f'] = maybeAutoLink
+		p.inlineCallback['H'] = maybeAutoLink
+		p.inlineCallback['M'] = maybeAutoLink
+		p.inlineCallback['F'] = maybeAutoLink
+	}
+	if p.extensions&Footnotes != 0 {
 		p.notes = make([]*reference, 0)
-		p.notesRecord = make(map[string]struct{})
 	}
-
-	first := firstPass(p, input)
-	second := secondPass(p, first)
-	return second
+	return &p
 }
 
-// first pass:
-// - normalize newlines
-// - extract references (outside of fenced code blocks)
-// - expand tabs (outside of fenced code blocks)
-// - copy everything else
-func firstPass(p *parser, input []byte) []byte {
-	var out bytes.Buffer
-	tabSize := TAB_SIZE_DEFAULT
-	if p.flags&EXTENSION_TAB_SIZE_EIGHT != 0 {
-		tabSize = TAB_SIZE_EIGHT
-	}
-	beg := 0
-	lastFencedCodeBlockEnd := 0
-	for beg < len(input) {
-		// Find end of this line, then process the line.
-		end := beg
-		for end < len(input) && input[end] != '\n' && input[end] != '\r' {
-			end++
-		}
+// Option customizes the Markdown processor's default behavior.
+type Option func(*Markdown)
 
-		if p.flags&EXTENSION_FENCED_CODE != 0 {
-			// track fenced code block boundaries to suppress tab expansion
-			// and reference extraction inside them:
-			if beg >= lastFencedCodeBlockEnd {
-				if i := p.fencedCodeBlock(&out, input[beg:], false); i > 0 {
-					lastFencedCodeBlockEnd = beg + i
-				}
-			}
-		}
-
-		// add the line body if present
-		if end > beg {
-			if end < lastFencedCodeBlockEnd { // Do not expand tabs while inside fenced code blocks.
-				out.Write(input[beg:end])
-			} else if refEnd := isReference(p, input[beg:], tabSize); refEnd > 0 {
-				beg += refEnd
-				continue
-			} else {
-				expandTabs(&out, input[beg:end], tabSize)
-			}
-		}
-
-		if end < len(input) && input[end] == '\r' {
-			end++
-		}
-		if end < len(input) && input[end] == '\n' {
-			end++
-		}
-		out.WriteByte('\n')
-
-		beg = end
+// WithRenderer allows you to override the default renderer.
+func WithRenderer(r Renderer) Option {
+	return func(p *Markdown) {
+		p.renderer = r
 	}
+}
 
-	// empty input?
-	if out.Len() == 0 {
-		out.WriteByte('\n')
+// WithExtensions allows you to pick some of the many extensions provided by
+// Blackfriday. You can bitwise OR them.
+func WithExtensions(e Extensions) Option {
+	return func(p *Markdown) {
+		p.extensions = e
 	}
-
-	return out.Bytes()
 }
 
-// second pass: actual rendering
-func secondPass(p *parser, input []byte) []byte {
-	var output bytes.Buffer
-
-	p.r.DocumentHeader(&output)
-	p.block(&output, input)
-
-	if p.flags&EXTENSION_FOOTNOTES != 0 && len(p.notes) > 0 {
-		p.r.Footnotes(&output, func() bool {
-			flags := LIST_ITEM_BEGINNING_OF_LIST
-			for i := 0; i < len(p.notes); i += 1 {
-				ref := p.notes[i]
-				var buf bytes.Buffer
-				if ref.hasBlock {
-					flags |= LIST_ITEM_CONTAINS_BLOCK
-					p.block(&buf, ref.title)
-				} else {
-					p.inline(&buf, ref.title)
-				}
-				p.r.FootnoteItem(&output, ref.link, buf.Bytes(), flags)
-				flags &^= LIST_ITEM_BEGINNING_OF_LIST | LIST_ITEM_CONTAINS_BLOCK
-			}
-
-			return true
+// WithNoExtensions turns off all extensions and custom behavior.
+func WithNoExtensions() Option {
+	return func(p *Markdown) {
+		p.extensions = NoExtensions
+		p.renderer = NewHTMLRenderer(HTMLRendererParameters{
+			Flags: HTMLFlagsNone,
 		})
 	}
+}
 
-	p.r.DocumentFooter(&output)
-
-	if p.nesting != 0 {
-		panic("Nesting level did not end at zero")
+// WithRefOverride sets an optional function callback that is called every
+// time a reference is resolved.
+//
+// In Markdown, the link reference syntax can be made to resolve a link to
+// a reference instead of an inline URL, in one of the following ways:
+//
+//  * [link text][refid]
+//  * [refid][]
+//
+// Usually, the refid is defined at the bottom of the Markdown document. If
+// this override function is provided, the refid is passed to the override
+// function first, before consulting the defined refids at the bottom. If
+// the override function indicates an override did not occur, the refids at
+// the bottom will be used to fill in the link details.
+func WithRefOverride(o ReferenceOverrideFunc) Option {
+	return func(p *Markdown) {
+		p.referenceOverride = o
 	}
+}
 
-	return output.Bytes()
+// Run is the main entry point to Blackfriday. It parses and renders a
+// block of markdown-encoded text.
+//
+// The simplest invocation of Run takes one argument, input:
+//     output := Run(input)
+// This will parse the input with CommonExtensions enabled and render it with
+// the default HTMLRenderer (with CommonHTMLFlags).
+//
+// Variadic arguments opts can customize the default behavior. Since Markdown
+// type does not contain exported fields, you can not use it directly. Instead,
+// use the With* functions. For example, this will call the most basic
+// functionality, with no extensions:
+//     output := Run(input, WithNoExtensions())
+//
+// You can use any number of With* arguments, even contradicting ones. They
+// will be applied in order of appearance and the latter will override the
+// former:
+//     output := Run(input, WithNoExtensions(), WithExtensions(exts),
+//         WithRenderer(yourRenderer))
+func Run(input []byte, opts ...Option) []byte {
+	r := NewHTMLRenderer(HTMLRendererParameters{
+		Flags: CommonHTMLFlags,
+	})
+	optList := []Option{WithRenderer(r), WithExtensions(CommonExtensions)}
+	optList = append(optList, opts...)
+	parser := New(optList...)
+	ast := parser.Parse(input)
+	var buf bytes.Buffer
+	parser.renderer.RenderHeader(&buf, ast)
+	ast.Walk(func(node *Node, entering bool) WalkStatus {
+		return parser.renderer.RenderNode(&buf, node, entering)
+	})
+	parser.renderer.RenderFooter(&buf, ast)
+	return buf.Bytes()
+}
+
+// Parse is an entry point to the parsing part of Blackfriday. It takes an
+// input markdown document and produces a syntax tree for its contents. This
+// tree can then be rendered with a default or custom renderer, or
+// analyzed/transformed by the caller to whatever non-standard needs they have.
+// The return value is the root node of the syntax tree.
+func (p *Markdown) Parse(input []byte) *Node {
+	p.block(input)
+	// Walk the tree and finish up some of unfinished blocks
+	for p.tip != nil {
+		p.finalize(p.tip)
+	}
+	// Walk the tree again and process inline markdown in each block
+	p.doc.Walk(func(node *Node, entering bool) WalkStatus {
+		if node.Type == Paragraph || node.Type == Heading || node.Type == TableCell {
+			p.inline(node, node.content)
+			node.content = nil
+		}
+		return GoToNext
+	})
+	p.parseRefsToAST()
+	return p.doc
+}
+
+func (p *Markdown) parseRefsToAST() {
+	if p.extensions&Footnotes == 0 || len(p.notes) == 0 {
+		return
+	}
+	p.tip = p.doc
+	block := p.addBlock(List, nil)
+	block.IsFootnotesList = true
+	block.ListFlags = ListTypeOrdered
+	flags := ListItemBeginningOfList
+	// Note: this loop is intentionally explicit, not range-form. This is
+	// because the body of the loop will append nested footnotes to p.notes and
+	// we need to process those late additions. Range form would only walk over
+	// the fixed initial set.
+	for i := 0; i < len(p.notes); i++ {
+		ref := p.notes[i]
+		p.addExistingChild(ref.footnote, 0)
+		block := ref.footnote
+		block.ListFlags = flags | ListTypeOrdered
+		block.RefLink = ref.link
+		if ref.hasBlock {
+			flags |= ListItemContainsBlock
+			p.block(ref.title)
+		} else {
+			p.inline(block, ref.title)
+		}
+		flags &^= ListItemBeginningOfList | ListItemContainsBlock
+	}
+	above := block.Parent
+	finalizeList(block)
+	p.tip = above
+	block.Walk(func(node *Node, entering bool) WalkStatus {
+		if node.Type == Paragraph || node.Type == Heading {
+			p.inline(node, node.content)
+			node.content = nil
+		}
+		return GoToNext
+	})
 }
 
 //
@@ -516,18 +486,56 @@ func secondPass(p *parser, input []byte) []byte {
 //
 // are not yet supported.
 
-// References are parsed and stored in this struct.
+// reference holds all information necessary for a reference-style links or
+// footnotes.
+//
+// Consider this markdown with reference-style links:
+//
+//     [link][ref]
+//
+//     [ref]: /url/ "tooltip title"
+//
+// It will be ultimately converted to this HTML:
+//
+//     <p><a href=\"/url/\" title=\"title\">link</a></p>
+//
+// And a reference structure will be populated as follows:
+//
+//     p.refs["ref"] = &reference{
+//         link: "/url/",
+//         title: "tooltip title",
+//     }
+//
+// Alternatively, reference can contain information about a footnote. Consider
+// this markdown:
+//
+//     Text needing a footnote.[^a]
+//
+//     [^a]: This is the note
+//
+// A reference structure will be populated as follows:
+//
+//     p.refs["a"] = &reference{
+//         link: "a",
+//         title: "This is the note",
+//         noteID: <some positive int>,
+//     }
+//
+// TODO: As you can see, it begs for splitting into two dedicated structures
+// for refs and for footnotes.
 type reference struct {
 	link     []byte
 	title    []byte
-	noteId   int // 0 if not a footnote ref
+	noteID   int // 0 if not a footnote ref
 	hasBlock bool
-	text     []byte
+	footnote *Node // a link to the Item node within a list of footnotes
+
+	text []byte // only gets populated by refOverride feature with Reference.Text
 }
 
 func (r *reference) String() string {
-	return fmt.Sprintf("{link: %q, title: %q, text: %q, noteId: %d, hasBlock: %v}",
-		r.link, r.title, r.text, r.noteId, r.hasBlock)
+	return fmt.Sprintf("{link: %q, title: %q, text: %q, noteID: %d, hasBlock: %v}",
+		r.link, r.title, r.text, r.noteID, r.hasBlock)
 }
 
 // Check whether or not data starts with a reference link.
@@ -535,7 +543,7 @@ func (r *reference) String() string {
 // (in the render struct).
 // Returns the number of bytes to skip to move past it,
 // or zero if the first line is not a reference.
-func isReference(p *parser, data []byte, tabSize int) int {
+func isReference(p *Markdown, data []byte, tabSize int) int {
 	// up to 3 optional leading spaces
 	if len(data) < 4 {
 		return 0
@@ -545,18 +553,18 @@ func isReference(p *parser, data []byte, tabSize int) int {
 		i++
 	}
 
-	noteId := 0
+	noteID := 0
 
 	// id part: anything but a newline between brackets
 	if data[i] != '[' {
 		return 0
 	}
 	i++
-	if p.flags&EXTENSION_FOOTNOTES != 0 {
+	if p.extensions&Footnotes != 0 {
 		if i < len(data) && data[i] == '^' {
 			// we can set it to anything here because the proper noteIds will
 			// be assigned later during the second pass. It just has to be != 0
-			noteId = 1
+			noteID = 1
 			i++
 		}
 	}
@@ -568,7 +576,11 @@ func isReference(p *parser, data []byte, tabSize int) int {
 		return 0
 	}
 	idEnd := i
-
+	// footnotes can have empty ID, like this: [^], but a reference can not be
+	// empty like this: []. Break early if it's not a footnote and there's no ID
+	if noteID == 0 && idOffset == idEnd {
+		return 0
+	}
 	// spacer: colon (space | tab)* newline? (space | tab)*
 	i++
 	if i >= len(data) || data[i] != ':' {
@@ -599,7 +611,7 @@ func isReference(p *parser, data []byte, tabSize int) int {
 		hasBlock              bool
 	)
 
-	if p.flags&EXTENSION_FOOTNOTES != 0 && noteId != 0 {
+	if p.extensions&Footnotes != 0 && noteID != 0 {
 		linkOffset, linkEnd, raw, hasBlock = scanFootnote(p, data, i, tabSize)
 		lineEnd = linkEnd
 	} else {
@@ -612,11 +624,11 @@ func isReference(p *parser, data []byte, tabSize int) int {
 	// a valid ref has been found
 
 	ref := &reference{
-		noteId:   noteId,
+		noteID:   noteID,
 		hasBlock: hasBlock,
 	}
 
-	if noteId > 0 {
+	if noteID > 0 {
 		// reusing the link field for the id since footnotes don't have links
 		ref.link = data[idOffset:idEnd]
 		// if footnote, it's not really a title, it's the contained text
@@ -634,15 +646,12 @@ func isReference(p *parser, data []byte, tabSize int) int {
 	return lineEnd
 }
 
-func scanLinkRef(p *parser, data []byte, i int) (linkOffset, linkEnd, titleOffset, titleEnd, lineEnd int) {
+func scanLinkRef(p *Markdown, data []byte, i int) (linkOffset, linkEnd, titleOffset, titleEnd, lineEnd int) {
 	// link: whitespace-free sequence, optionally between angle brackets
 	if data[i] == '<' {
 		i++
 	}
 	linkOffset = i
-	if i == len(data) {
-		return
-	}
 	for i < len(data) && data[i] != ' ' && data[i] != '\t' && data[i] != '\n' && data[i] != '\r' {
 		i++
 	}
@@ -705,13 +714,13 @@ func scanLinkRef(p *parser, data []byte, i int) (linkOffset, linkEnd, titleOffse
 	return
 }
 
-// The first bit of this logic is the same as (*parser).listItem, but the rest
+// The first bit of this logic is the same as Parser.listItem, but the rest
 // is much simpler. This function simply finds the entire block and shifts it
 // over by one tab if it is indeed a block (just returns the line if it's not).
 // blockEnd is the end of the section in the input buffer, and contents is the
 // extracted text that was shifted over one tab. It will need to be rendered at
 // the end of the document.
-func scanFootnote(p *parser, data []byte, i, indentSize int) (blockStart, blockEnd int, contents []byte, hasBlock bool) {
+func scanFootnote(p *Markdown, data []byte, i, indentSize int) (blockStart, blockEnd int, contents []byte, hasBlock bool) {
 	if i == 0 || len(data) == 0 {
 		return
 	}