Syntax Diagram Conventions

The reference section includes diagrams describing the syntax of the elements in a syndication file. The diagrams look something like this:

    (source="text" sourceid="text")?

In these diagrams, anything appearing in plain black characters is literal content: that is, it should be entered in the file exactly as shown. Anything appearing in black, italic characters is a placeholder that must be replaced by something else. The only such placeholder currently in use is:


This placeholder can be replaced by any element. This is mainly intended to allow you to enter HTML elements in the body of field elements. You can, however, insert elements from any other namespace if you have the need.

Anything appearing in this color is neither literal content nor a placeholder, but has one of the following special meanings:



  • A set of elements or attributes that are to be regarded as a group, A ?, * or + following the closing ) applies to the whole group.

  • A set of alternatives separated by | characters, only one of which may be selected.


Separates the alternatives in a () set.


Indicates that the preceding element is optional.


Indicates that the preceding element may appear 0 or more times.


Indicates that the preceding element may appear 1 or more times.


Represents possible content in an element or attribute.

Element order is not significant. The syntax diagram shown above seems to suggest that a sectionref element must appear before a relation element, but this is not the case: the elements can in fact appear in any order.