Most of the discussion on this thread has dealt with the relevance of the Bold button on FrameMaker's Text Formatting toolbar to structured documents.
While someone made the suggestion to create a <b> element and then insert text within the new element, I don't think anyone has yet commented on how easy it is to wrap an element (<b> or another element) around existing content. You can do so with the Element Catalog. Simply select the content to be wrapped and double-click the tag of the new element (e.g., b) in the Element Catalog. Or click the tag in the Element Catalog and then the Wrap button at the bottom of the Catalog.
If you prefer to use the keyboard, you can use what is called Smart Insert in FM 11 and quick keys in earlier versions. The first three buttons at the bottom of the Element Catalog window are Insert, Wrap, and Change. You don't need to have the Catalog open to use Smart Insert. I mentioned the buttons only because that order is pretty easy to remember--1. Insert, 2. Wrap, 3. Change. The keyboard shortcuts Ctrl-1, Ctrl-2, and Ctrl-3 bring up the Smart Insert or Quick Keys to Insert, Wrap, or Change an element. With Smart Insert, a pop-up menu appears that shows the available elements. You can use the up and down arrow keys to navigate to the one you want, or type a unique prefix. Then press Enter to perform the operation (or Esc to cancel). With Quick Keys, the left side of the status bar at the bottom of the document window or Structure View (whichever is current) will prompt for the element tag with I: for Insert, W: for Wrap or C: for Change. Again, use the arrow keys or a prefix to display the desired element tag and then press Enter.
So, to create a new <b> element to hold an existing string, select the string, type Ctrl-2 b, and press Enter.
That said, I will close with an observation on the use of format overrides in structured documents. While automatic formatting based on element structure is the heart of structured FM, the software was deliberately designed in recognition that as a practical matter it is sometimes necessary for an author to create formatting that the document's element definitions simply do not provide. It therefore allows the user to tweak the formatting (for example, by deliberating making some content bold without using the element structure to do so). Users should understand the difference between element-based formatting and format overrides and use the latter with care if at all.
--Lynne