html.grammar

start top { element* }

element {
  comment | doctype | tag | entity | text
}

comment="comment" {
  "<!--" (!"-->" _)* "-->"
}

doctype="meta" {
  ("<!doctype" | "<!DOCTYPE") !wordChar (!">" _)* ">"
}

context tag {
  openTag
  (asTag("/>") |
   &selfClosing asTag(">") |
   asTag(">") element* (~"</" (&matchingTag closeTag)?))
}

context openTag {
  asTag("<") !(spaceChar* "/") spaceChar* tagName spaceChar* attribute*
}

context closeTag {
  asTag("</") spaceChar* tagName asTag(">")
}

asTag(value)="tag" { value }

attribute {
  attributeName spaceChar* ("=" spaceChar* attributeValue)? spaceChar*
}

attributeValue="string" {
  "\"" (!"\"" _)* "\"" |
  "'" (!"'" _)* "'" |
  (!(spaceChar | ">") .)*
}

entity="atom" {
  "&" (!(";" | spaceChar) .)* ";"
}

text {
  "\n" | (!("&" | "<") .)+
}

tagName="tag" { wordChar+ }
attributeName="attribute" { wordChar+ }

wordChar { "a"-"z" | "A"-"Z" | "-" | "." | "0"-"9" | "_" }

spaceChar { "\n" | "\t" | " " }