From Microformats Wiki
hcalendar-brainstorming /
Revision as of 02:30, 1 September 2005 by Tantek (talk | contribs) (notes on VTODO)
Jump to navigation Jump to search




Along with the four base properties, you can define addtional properties through the use of the x-prop property. For best-practices for hCal to iCal transformers, it would be helpful if the transforming application added the following x-* properties:

  • X-FROM-URL. The value of this property would be the URL of the page where the iCal representation was generated.
  • X-WR-CALNAME. iCal.app recognizes this property as the "calendar name" for subscribed calendars. Thus transforming applications *should* take the <title>...</title> from the page being parsed, optionally append " events", and use that value for the X-WR-CALNAME property in the resulting feed. E.g. if the page had <title>Example Home Page</title> then the .ics output should have as part of the vcalendar object:
X-WR-CALNAME:Example Home Page


This is a growing example case written in iCal format and transformed to the corresponding XHTML. These conversions are open to community input.

SUMMARY: Short Title
DESCRIPTION: Full Description
<p class="vevent">
<!-- @@ how to deal with Whitespace issues in lists 'foo, bar' -->
<ul class="categories">
<a href="http://example.com" class="summary">Short Title</a>
<span class="description">description</span>
<span class="geo"><span class="Lat">37.386013</span> <span class="Lon">-122.082932</span></span>

<!-- This currently does not take into consideration the VALUE=DATE -->
<!-- The transforming application could attempt to detect the proper format and add params as needed? -->
Date: <em class="dtstart">20040101</em> - <em class="dtend">20040101T235959Z</em>

<!-- any thoughts to better encode attendee -->
<!-- the ROLE must be of a known type, but one of type is x-name (user-specified) -->
<!-- therefore there is no solid way to know "chair" refers to a ROLE parameter -->
<a class="attendee chair" href="mailto:JohnDoe@example.com">John Doe</a>

<!-- this messy, but works. Is there a better way? -->
<p class="rrule">The event will be held <span class="freq">yearly</span> until <span class=""until">20080102T000000Z</span>.</p>


@@-need to look at nested tag examples

<span class="description"><span class="summary">Short Title</span> to a longer article</span>

SUMMARY:Short Title
DESCRIPTION:Short Title to a longer article

Examples from RFC 2445

With the abbr's title attribute being used rather than the node value, the actual data could vary and still represent the same vcalendar.

PRODID:-//hacksw/handcal//NONSGML v1.0//EN
SUMMARY:Bastille Day Party
<span class="vcalendar">
  <span class="vevent">
    <abbr class="dtstart" title="19970714T170000Z">July 14th</abbr>
    <abbr class="dtend" title="19970715T035959Z"></abbr>
    <span class="summary">Bastille Day Party</span>

The UID in iCal is represented in HTML as the id attribute in these examples. Any valid id in HTML is a valid UID in iCal, but not the contrapositive, a valid UID is NOT a valid HTML id. HTML ids can only start with a letter, not a number.

SUMMARY:Annual Employee Review

<pre><nowiki> <span class="vcalendar"> <span class="vevent" id="19970901T130000Z-123402@host.com"> <abbr title="dtstamp" class="19970901T1300Z"></abbr> <abbr title="dtstart" class="19970903T163000Z">September 3rd, 4:30pm</abbr>- <abbr title="dtend" class="19970903T190000Z">7:00pm</abbr> <span class="summary">Annual Employee Review</span> <span class="class">private</span> <ul class="categories"> <li>BUSINESS</li> <li>HUMAN RESOURCES</li> </ul> </span> </span>

SUMMARY:Laurel is in sensitivity awareness class.
<span class="vcalendar">
  <span class="vevent" id="19970901T130000Z-123402@host.com">
    <abbr title="dtstamp" class="19970901T1300Z"></abbr>
    <abbr title="dtstart" class="19970401T163000Z">April 1st 4:30pm</abbr>-
    <abbr title="dtend" class="19970402T010000Z">1:00am</abbr>
    <span class="summary">Laurel is in sensitivity awareness class.</span>
    <span class="class">PUBLIC</span>
    <ul class="categories">
      <li>HUMAN RESOURCES</li>
    <span class="transp">Transparent</span>

@@ The way RRULE is encoded should be discussed.

SUMMARY:Our Blissful Anniversary
<span class="vcalendar">
  <span class="vevent" id="19970901T130000Z-123403@host.com">
    <abbr title="dtstart" class="19970901T1300Z"></abbr>
    <abbr title="dtend" class="19971102">November 2nd</abbr>
    <span class="summary">Our Blissful Anniversary</span>
    <span class="class">CONFIDENTIAL</span>
    <ul class="categories">
      <li>SPECIAL OCCASION</li>
    <span class="rrule"><span class="freq">YEARLY</span></span>

Examples from real world event sites

Laughing Squid

Laughing Squid had the following multiple occurence event example:

Thu, Apr 7 : Tu/Wed: 12-4pm Th/Fr/Sat 12-7pm Sun 12-6pm 

In addition, later on in the description, it says:

April 7-21, 2005

This is actually quite a non-trivial example, because the event lasts for different durations on different days (4 hours, 7 hours, 6 hours).

Because of the differing durations, the specification requires that *each* instance of this recurring event be explicitly specified.

But first we markup the starting date and time explicitly:

<abbr class="dtstart" title="20050407T1200-0700">Thu, Apr 7</abbr> : 

Then we put in the quite lengthy explicit specification of every other time the event occurs, marked up around the human readable description.

<abbr class="rdate" title="20050407T1200-0700/PT7H, 20050408T1200-0700/PT7H, 
20050409T1200-0700/PT7H, 20050410T1200-0700/PT6H, 20050412T1200-0700/PT4H, 
20050413T1200-0700/PT4H, 200504014T1200-0700/PT7H, 20050415T1200-0700/PT7H, 
20050416T1200-0700/PT7H, 20050417T1200-0700/PT6H, 20050419T1200-0700/PT4H, 
20050420T1200-0700/PT4H, 20050421T1200-0700/PT7H" >
Tu/Wed: 12-4pm Th/Fr/Sat 12-7pm Sun 12-6pm

The RDATE "PERIOD" format is fairly straightforward. You simply list *each* occurrence of the event, separated by commas. Each occurrence consists of the ISO8601 datetime of the start of the event, followed by a slash "/", followed by *either* the duration of the event (e.g. 7 hours = PT7H), *or* a complete ISO8601 datetime of the end of the event. I chose to use the duration of the event for this example for reason of brevity.

Note that "value=period:" is unnecessary in the rdate value since the parser can infer "value=period:" from the presence of a "/" in the title attribute value.

With simpler repeating events, or perhaps events which only repeat a day or two, their hCalendar markup may be more illustrative of how to do this in a general way.

CSS Styles

Since the hCal properties are added in as CSS styles, you can style them along with any normal CSS style. You are free to style these properties in any fashion you want, but here are a few examples that you can use.

Hiding Data

If you want to encode additional data without it being displayed in the HTML, you can use the CSS style property 'display'.

<span style="display:none">Hidden Data</span>

This data will be found by any transforming application and will be properly encoded into an iCal file.

Preserving White-space

If you are encoding data that requires tabs, returns, or other white-space to be perserved you can use the following CSS property to do so in HTML.

<span style="white-space: pre">
This white-space
will be

white-space can take one of three different parameters; normal, pre, and no-wrap.


How to include hCal encodings into your favourite Blogging Software.

Open Questions

General Questions

Q: Should Transforming applications purely extract the information and ignore validity? or should there be some checking, or should this be left to the importing application? (i.e. DTSTART;VALUE=DATE: This-Is-Not-a-proper-date)

A: The simpler the better. Other than checking for perhaps X(HT)ML validity, it should be a simple translator, because presumably the receiving iCalendar application has to have malformed .ics handling already. Let's avoid duplicating that. -- Tantek Çelik

Q: What about multiple of the instances same vCal entity? (two instances of DTSTART) Is this left up to the importing application, or should the XSLT transformation fail?

A: Same as previous. Leave it up to the importing application to interpret it per the iCalendar spec, e.g. what does RFC2445 say about two instances of DTSTART? -- Tantek Çelik

From RFC2445: 4.1.2 Multiple Values Some properties defined in the iCalendar object can have multiple values. The general rule for encoding multi-valued items is to simply create a new content line for each value, including the property name. However, it should be noted that some properties support encoding multiple values in a single property by separating the values with a COMMA character (US-ASCII decimal 44). Individual property definitions should be consulted for determining whether a specific property allows multiple values and in which of these two forms.

Other than that, it does not mention what to do ABOUT invalid data, or which of the multiple entries takes precedence. The only mention of duplicate instances is in the RRULE and EXDATE rules where events exclusions/inclusions overlap. Then duplicate instances are ignore. If it is explicitly written for those items, but NOT for things like DTSTART, then it is difficult to assume duplicate instances are ignored for them as well.

Each of the Components (VEVENT, ...) define which properties can exisit and in what quantity. So multiple DTSTART properties are NOT allowed. -- Brian Suda

Q: Should vCal entitles be represented in XHTML in classes ONLY on block-level element? or should some like VEVENT be block-level and others be of any? does this impact the semantics at all?

A: I don't think the (X)HTML notion of "block-level" should have any bearing whatsoever on vCal entities. You should be able to say

and either should work.

Q: Should the transforming application add any additional information to the iCalendar representation other than what was encoded in the HTML? (i.e. UID, the unique identifier might not be present in the HTML code, but could be generated by the transforming application and added to the iCal file. Should this be allowed? or should the transforming app ONLY be allowed to add X-PROPERTY properties?) IF it was not explicitly encoded in the HTML should it be left out? What about default values?

Q: If we are looking at the most semantic way to encoding iCalendar data in HTML then several other attributes should be considered besides just 'class'. There are two other candidated, ID and REL. The ID tag MUST be unique within the XHTML file (this could be used for the UID property). The REL attribute can ONLY be applied to 'a' and 'link' tags, but might be helpful. Are namespac<ETH>H �n option? xml:lang, xml:base, are there any others that might be more semantically correct to encode this data?

Q: To help distinguish xparam values from other actual CSS styles, should we assume/mandate that all values in a class attribute within an encoded iCal component class attribute (<x class="vevent|vtodo|...">) be considered an xparam?

A: If you are using other CSS styles (e.g. "center", "bluebox", "greenline", etc.) nested within an iCal component, those should be avoided and the styles applied to the list of iCal properties instead/also?

.center, .vevent { text-align: center; }

Encoding Questions

The way dates are encoded is not always the most user friendly. If i want to encode january 1st, 2005, that is 20050101, which is displayed as 20050101. If we are marking-up comma seperated values, like FN, with each sub-element inside their own tag, then the date should be allowed the same.

(However, FN is in the RFC2426 spec and vCard schema, these individual date terms are not, therefore the reasoning in the last sentence is incorrect. -Tantek)

<span class="dtstart"><span class="Year">2005</span><span class="Month">01</span><span class="Day">01</span></span>

With this encoding, then YYYYMMDD schema can be rearranged for different cultures, DD-MM-YYYY for UK, MM-DD-YYYY for US, etc.

<span class="dtstart"><span class="Month">02</span>-<span class="Day">01</span>-<span class="Year">2005</span></span>
<span class="dtstart"><span class="Day" title="first">01</span>-<span class="Month" title="Feb">02</span>-<span class="Year">2005</span></span>

Both of the above encodings are equal, the '-' seperator is ignored by the transforming application. -- Brian Suda

Agreed that the way dates are encoded is not always the most user friendly, but there is an easier solution to this, once you think of what is actually going on in the difference between ISO8601 dates, and dates the way humans use them. Humans typically use an abbrevation or shorthand for a date, like "tomorrow", or "Tuesday", or "the 4th", or perhaps "July 4th". Thus it makes sense to permit this in hCalendar, using the <abbr> tag which provides the ability to markup the human-familiar short form of some data or language, while preserving the long form in the 'title' attribute.

E.g. for the above example of a start date of January 1st, 2005, you could use this markup:

<abbr class="dtstart" title="20050101">January 1st, 2005</abbr>

Which would display as January 1st, 2005 but would provide the respective ISO8601 date in the title attribute. - Tantek


A HTML head profile needs creation and a home.


A simple implementation of transforming/extracting vCal data from an XHTML file is available for testing. A bookmarklet is also available. The code will be updated as the spec is finalised. http://suda.co.uk/projects/X2V/

Relationships with other microformats

In a Technology Review interview, TBL said "It would have the relationships between the event and the various people chairing it.".

We should have examples of how hCalendar events can indicate such relationships, both in the format and in the presentation. E.g.:

* Would it just link to URLs for the various people?  (e.g. to their homepages/blogs etc.)
* Would it include hCards for the various people?  
* Would it link to hCards for various people?
* Perhaps allow all the above?


According to RFC2445, the proposed media type value is 'text/calendar'.

A standard vCalendar file has an extension of .vcs and MIME type of text/x-vCalendar. If you use iCalendar, the MIME type is "text/Calendar" and the extension is .ics.

Text/X-vCalendar Content Type The vCalendar object can also be passed as a non-standard MIME media type. This would be useful in order to clearly identify the vCalendar object in an electronic mail message body part. A non-standard, vCalendar object should be identified as the MIME type/subtype "text/x-vCalendar".

@@ - i have to do some more investigation, but (i think) vCalendar is a subset of iCalendar, so many of the same encodings will work for both, but this document is dealing with iCalendar RFC2445 representation!


We need to come up with a nice [ hCal | friendly ] button to indicate that event info on a page/site is using hCalendar. - Tantek.


  • [ hCal | friendly ]
  • [ hCal | aware ]
  • [ hCal | inside ]
  • [ Valid | hCalendar ] - though that would require writing an hCalendar validator which people could link to.
  • [ <icon> | hCalendar ] where <icon> could be some generic calendar looking thing, or it could be a PHP generated image with the actual date in the icon, kind of like how the Apple iCal icon updates in the dock automatically.

And then we have to pick colors and all that stuff - Tantek.

Other ideas:

  • [ hCal | enabled ]
  • [ hCal | available ] - kind of an off-hand reference to being available for meetings, etc.

- Eric

Including More of iCalendar

Free/Busy information

See Neil Jensen's analysis of how to represent the iCalendar VFREEBUSY object in hCalendar.

In order to show free/busy information, we could either use the existing vevent class (with empty location, summary, etc. properties) or create a new vfreebusy class. We should create a new vfreebusy class because it is consistent with the XHTML design principles, particularly point #4, "Use class names based on names from the original schema...".

In the iCalendar standard, the vfreebusy calendar component frequently has more than one freebusy property, and also may have a number of other properties such as organizer. For example:


So, our hCalendar representation should include separate elements for the vfreebusy calendar component (defined once) and the freebusy property (possibly defined many times):

 <span class="vfreebusy"> 
 <div class="freebusy"> 
 <abbr class="dtstart" title="20050721T1000-0800"> 
 July 21, 2005 - 10:00 
 </abbr> - 
 <abbr class="dtend" title="20050721T1100-0800"> 
 <div class="freebusy"> 
 <abbr class="dtstart" title="20050722T1000-0800"> 
 July 22, 2005 - 10:00 
 </abbr> - 
 <abbr class="dtend" title="20050722T1100-0800"> 

According to RFC2445, "When publishing a "VFREEBUSY" calendar component, the property is used to specify the calendar that the published busy time came from." The property type is CAL-ADDRESS, and can include "non-standard, language, common name and directory entry reference" property parameters. CAL-ADDRESS is "...a URI as defined by [RFC 1738] or any other IANA registered form...".

From what I've seen, Microsoft Outlook typically populates this property with the email address of the calendar owner, which initially made me think of using hCard to specify the organizer. However, given that the property refers to the calendar and not necessarily the person who owns or has published it, I think we should use a new organizer element, as shown below:



 <span class="vfreebusy"> 
 organizer: <span class="organizer">jsmith@host.com</span> 
 <div class="freebusy"> 
 <abbr class="dtstart" title="20050314T133000Z"> 
 March 14, 2005 - 13:30 
 </abbr> - 
 <abbr class="dtend" title="20050314T163000Z"> 

Hmmm, this looks a little funny when the organizer is so obviously an email address, but at least it is semantically correct. The other problem that I can now see occurring is when the organizer property has parameters, for example (from the iCalendar spec):


Perhaps it's best to use the same approach described in "Human vs. ISO8601 dates problem solved"; use the abbr element like so:

 <span class="vfreebusy"> 
 <div class="freebusy"> 
 organizer: <abbr class="organizer" title="CN=JohnSmith;DIR=ldap://host.com:6666/o=3DDC%20Associ 
 <abbr class="dtstart" title="20050314T133000Z"> 
 March 14, 2005 - 13:30 
 </abbr> - 
 <abbr class="dtend" title="20050314T163000Z"> 

To-Do information

The Policy Aware Web (PAW) Project Meeting - 23 Aug 2005 uses class="vtodo" to capture action items. Clearly recording action items from a meeting and publishing them as minutes is a good practical example use of the VTODO object on the web.

What's the scenario for usage though?

What kind of indexer/aggregator application would find these VTODO items and what would it do with them?

Perhaps with some way of figuring out who the to-do item is assigned to ("ATTENDEE"), who assigned it ("DELEGATED-FROM"), and a whitelisting of who, perhaps the "ORGANIZER" property, (and their domains/URLs) that a user would accept assignments from, a user could aggregate to-do items assigned from other folks. Then question remains how to update the status ("STATUS") (RFC 2445 Status) on that to-do item when it is (a) completed ("COMPLETED"), (b) abandoned/cut/rejected ("CANCELLED"), (c) some progress is made ("IN-PROCESS") etc. There certainly seems to be sufficient expressiveness in VTODO and its properties to do a decentralized to-do list / task distribution system. Could be very interesting for helping open source projects and other distributed teams do project management using the Web.


Normative References

Informative References

Other Implementations/Ideas