microformats2-parsing

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<entry-title>microformats2 parsing specification</entry-title>

Tantek Çelik (Editor)

microformats2 is a simple, open format for marking up data in HTML. The microformats2 parsing specification describes how to implement a microformats2 parser.

One of the goals of microformats2 is to greatly simplify parsing of microformats, in particular, by making parsing independent of any one vocabulary. This specification documents the microformats2 parsing algorithm for doing so.

Per CC0, to the extent possible under law, the editors have waived all copyright and related or neighboring rights to this work. In addition, as of 2024-11-22, the editors have made this specification available under the Open Web Foundation Agreement Version 1.0.

algorithm

parse a document for microformats

To parse a document for microformats, follow the HTML parsing rules and do the following:

  • start with an empty JSON "items" array and "rels" & "rel-urls" hashes:
{
 "items": [],
 "rels": {},
 "rel-urls": {}
}
  • parse the root element for class microformats, adding to the JSON items array accordingly
  • parse all hyperlink (<link> <a>) elements for rel microformats, adding to the JSON rels & rel-urls hashes accordingly
  • return the resulting JSON

Parsers may simultaneously parse the document for both class and rel microformats (e.g. in a single tree traversal).

parse an element for class microformats

To parse an element for class microformats:

  • parse element class for root class name(s) "h-*" and backcompat root classes
    • if not found, parse child elements for microformats (depth first, doc order)
    • else if found, start parsing a new microformat
      • create a new { } structure with:
        • type: [array of microformat "h-*" type(s) on the element],
        • properties: { } - to be filled in when that element itself is parsed for microformats properties
        • if that element is an <area> element, also add:
          • shape: from area[shape] if any
          • coords: from area[coords] if any
        • end if
      • parse child elements (document order) by:
        • parse a child element class for property class name(s) "p-*,u-*,dt-*,e-*" respectively as detailed below
        • if such class(es) are found, it is a property element
          • add properties found to current microformat's properties: { } structure
        • parse a child element for microformats (recurse)
          • if that child element itself has a microformat ("h-*" or backcompat roots) and is a property element, add it into the array of values for that property as a { } structure, add to that { } structure:
            • value:
              • if it's a p-* property element, use the first p-name of the h-* child
              • else if it's an e-* property element, re-use its { } structure with existing value: inside.
              • else if it's a u-* property element and the h-* child has a u-url, use the first such u-url
              • else use the parsed property value per p-*,u-*,dt-* parsing respectively
          • else add found elements that are microformats to the "children" array
      • imply properties for the found microformat (see below)

parse an element for properties

parsing a p- property

To parse an element for a p-x property value:

  • parse the element for the value-class-pattern, if a value is found then return it.
  • if abbr.p-x[title], then return the title attribute
  • else if data.p-x[value] or input.p-x[value], then return the value attribute
  • else if img.p-x[alt] or area.p-x[alt], then return the alt attribute
  • else return the textContent of the element, replacing any nested <img> elements with their alt attribute if present, or otherwise their src attribute if present, resolving any relative URLs, and removing all leading/trailing whitespace.

parsing a u- property

To parse an element for a u-x property value:

  • if a.u-x[href] or area.u-x[href], then get the href attribute
  • else if img.u-x[src] or audio.u-x[src] or video.u-x[src] or source.u-x[src], then get the src attribute
  • else if object.u-x[data], then get the data attribute
  • if there is a gotten value, return the normalized absolute URL of it, following the containing document's language's rules for resolving relative URLs (e.g. in HTML, use the current URL context as determined by the page, and first <base> element if any).
  • else parse the element for the value-class-pattern, if a value is found then return it.
  • else if abbr.u-x[title], then return the title attribute
  • else if data.u-x[value] or input.u-x[value], then return the value attribute
  • else return the textContent of the element after removing all leading/trailing whitespace.

parsing a dt- property

To parse an element for a dt-x property value:

  • parse the element for the value-class-pattern including the date and time parsing rules, if a value is found then return it.
  • if time.dt-x[datetime] or ins.dt-x[datetime] or del.dt-x[datetime], then return the datetime attribute
  • else if abbr.dt-x[title], then return the title attribute
  • else if data.dt-x[value] or input.dt-x[value], then return the value attribute
  • else return the textContent of the element after removing all leading/trailing whitespace.

parsing an e- property

To parse an element for a e-x property value:

  • return a dictionary with two keys:
    • html: the innerHTML of the element by using the HTML spec: Serializing HTML Fragments algorithm, with leading/trailing whitespace removed.
    • value: the textContent of the element, replacing any nested <img> elements with their alt attribute if present, or otherwise their src attribute if present, resolving the URL if it’s relative.

parsing for implied properties

To imply properties: (where h-x is the root microformat element being parsed)

  • if no explicit "name" property,
  • then imply by:
    • if img.h-x or area.h-x, then use its alt attribute for name
    • else if abbr.h-x[title] then use its title attribute for name
    • else if .h-x>img:only-child[alt]:not[.h-*] then use that img alt for name
    • else if .h-x>area:only-child[alt]:not[.h-*] then use that area alt for name
    • else if .h-x>abbr:only-child[title] then use that abbr title for name
    • else if .h-x>:only-child>img:only-child[alt]:not[.h-*] then use that img alt for name
    • else if .h-x>:only-child>area:only-child[alt]:not[.h-*] then use that area alt for name
    • else if .h-x>:only-child>abbr:only-child[title] use that abbr title for name
    • else use the textContent of the .h-x for name
    • drop all leading and trailing white-space from name
  • if no explicit "photo" property,
  • then imply by:
    • if img.h-x[src] then use src for photo
    • else if object.h-x[data] then use data for photo
    • else if .h-x>img[src]:only-of-type:not[.h-*] then use that img src for photo
    • else if .h-x>object[data]:only-of-type:not[.h-*] then use that object data for photo
    • else if .h-x>:only-child>img[src]:only-of-type:not[.h-*] then use that img src for photo
    • else if .h-x>:only-child>object[data]:only-of-type:not[.h-*] then use that object data for photo
    • if there is a gotten photo value, return the normalized absolute URL of it, following the containing document's language's rules for resolving relative URLs (e.g. in HTML, use the current URL context as determined by the page, and first <base> element if any).
  • if no explicit "url" property,
  • then imply by:
    • if a.h-x[href] or area.h-x[href] then use that [href] for url
    • else if .h-x>a[href]:only-of-type:not[.h-*] then use that [href] for url
    • else if .h-x>area[href]:only-of-type:not[.h-*] then use that [href] for url
    • if there is a gotten url value, return the normalized absolute URL of it, following the containing document's language's rules for resolving relative URLs (e.g. in HTML, use the current URL context as determined by the page, and first <base> element if any).

Note: The same markup for a property should not be causing that property to occur in both a microformat and one embedded inside - such a property should only be showing up on one of them. The parsing algorithm has details to prevent that, such as the :not[.h-*] tests above.

parse a hyperlink element for rel microformats

To parse a hyperlink element for rel microformats: (where * is the hyperlink element), use the following algorithm or an algorithm that produces equivalent results:

  • if the "rel" attribute of the element is empty then exit
  • set url to the value of the "href" attribute of the element, normalized to be an absolute URL following the containing document's language's rules for resolving relative URLs (e.g. in HTML, use the current URL context as determined by the page, and first <base> element if any).
  • treat the "rel" attribute of the element as a space separate set of rel values
  • for each rel value (rel-value)
    • if there is no key rel-value in the rels hash then create it with an empty array as its value
    • if url is not in the array of the key rel-value in the rels hash then add url to the array
  • end for
  • if there is no key with name url in the top-level "rel-urls" hash then add a key with name url there, with an empty hash value
  • add keys to the hash of the key with name url for each of these attributes (if present) and key not already set:
    • "hreflang": the value of the "hreflang" attribute
    • "media": the value of the "media" attribute
    • "title": the value of the "title" attribute
    • "type": the value of the "type" attribute
    • "text": the text content of the element if any
  • if there is no "rels" key in that hash, add it with an empty array value
  • set the value of that "rels" key to an array of all unique items in the set of rel values unioned with the current array value of the "rels" key
  • if the set of rel values has "alternate" this entire if clause may be dropped due to dropping alternates
    • if there's no top-level "alternates" array, then create it as an empty array.
    • add a new hash to the top-level "alternates" array with keys for each of these attributes when present:
      • "url": url
      • "rel": the set of rel values appended with spaces, except "alternate"
      • "hreflang": the value of the "hreflang" attribute
      • "media": the value of the "media" attribute
      • "title": the value of the "title" attribute
      • "type": the value of the "type" attribute
      • "text": the text content of the element if any
  • end if

rel parse examples

Here are some examples to show how parsed rels may be reflected into the JSON (empty items key).

E.g. parsing this markup: 

<a rel="author" href="http://example.com/a">author a</a>
<a rel="author" href="http://example.com/b">author b</a>
<a rel="in-reply-to" href="http://example.com/1">post 1</a>
<a rel="in-reply-to" href="http://example.com/2">post 2</a>
<a rel="alternate home"
   href="http://example.com/fr"
   media="handheld"
   hreflang="fr">French mobile homepage</a>

Would generate this JSON: 

{
  "items": [],
  "rels": { 
    "author": [ "http://example.com/a", "http://example.com/b" ],
    "in-reply-to": [ "http://example.com/1", "http://example.com/2" ],
    "alternate": [ "http://example.com/fr" ], 
    "home": [ "http://example.com/fr" ] 
  },
  "rel-urls": {
    "http://example.com/a": {
      "rels": ["author"], 
      "text": "author a"
    },
    "http://example.com/b": {
      "rels": ["author"], 
      "text": "author b"
    },
    "http://example.com/1": {
      "rels": ["in-reply-to"], 
      "text": "post 1"
    },
    "http://example.com/2": {
      "rels": ["in-reply-to"], 
      "text": "post 2"
    },
    "http://example.com/fr": {
      "rels": ["alternate", "home"],
      "media": "handheld", 
      "hreflang": "fr", 
      "text": "French mobile homepage"
    }
  }
  "alternates": [{
     "url": "http://example.com/fr", 
     "rel": "home", 
     "media": "handheld", 
     "hreflang": "fr",
     "text": "French mobile homepage"
  }]
}
⚠️ Warning: The "alternates" collection is likely to be dropped. Use "rel-urls" instead.


what do the CSS selector expressions mean

This section is non-normative.

Use SelectORacle to expand any of the above CSS selector expressions into longform English prose.

Exception:

  • :not[.h-*] is not a valid CSS selector but is used here to mean:
    • does not have any class names that start with "h-"

note HTML parsing rules

This section is non-normative.

microformats2 parsers are expected to follow HTML parsing rules, which includes for example:

questions

See the FAQ:

issues

See the issues page:

implementations

There are open source microformats2 parsers available for Javascript, node.js, PHP, Ruby and Python.

test suite

See:

Ports to/for other languages encouraged.

see also
Retrieved from "http://microformats.org/wiki/index.php?title=microformats2-parsing&oldid=65050"