Dear Wild,
A container element a structured document can either be a paragraph element, that contains one or more complete FrameMaker paragraphs (elements corresponding to chapters, titles, and list items, for instance, are typically paragraph elements), or a text range element, with content that comprises part of a paragraph. An EDD doesn't need to identify paragraph elements since containers are paragraphs by default. You make an element a text range with a text format rule that specifies TextRangeFormatting.
In your case, if you have a wrapper element that contains the three elements you want to appear on a single line, in the EDD, add a text format rule for the three inline elements that specifies TextRangeFormatting; specify the formatting of the overall paragraph in the element definition for the wrapper. If you don't have a wrapper, though, the overall paragraph will inherit formatting from whatever the containing element is; the containing element may be the document's root element or a major division such as a chapter or section. If that element's formatting is not what you want here, you can leave the "inline" elements as separate paragraph so that you can specify their formatting, but make the first two run-in heads (which is done in the Placement property of the pagination properties).
--Lynne