The phrase "are only outlined" is correct and usable in written English.
It can be used when indicating that something is described in a general or superficial manner without going into detail.
Example: "The main points of the project are only outlined in the initial proposal, and further details will be provided later."
Alternatives: "are merely sketched" or "are just summarized".
Right now the chairman's plan is only outlined in broad strokes, but the NPRM will be provided publicly tomorrow, at which point more (and more technical) commentary will begin.
Because the multiple-VI training protocol is also described in detail in that report, it is only outlined here.
The arrangement of mesogleal fibres is more complex and is only outlined in Figure 8 for those located in the equatorial plane.
The information provided to participants about the proposed data linkage was only outlined in summary as it was hoped that participants would help to shape the proposed data linkage by suggesting data for linkage and relevant barriers without being influenced by the background information provided.
Now there are only outlines of the wooden porches and stairs, and the embankments and front yards have been rebuilt.
"I don't believe I can take a decision [today] because the plans for the four-storey building on the greenfield section at the bottom of the development are only outline and I need more detail to make a judgement.
There were only outlines.
None of this action felt remotely believable, or theatrically urgent: here there were only outlines of ideas, at best, performed but never inhabited by the cast.
As he stumbles about at the behest of others, aspects of his wider world are only briefly outlined, such as, for example, the casual amalgamation of fast-food chains and political parties – a conceit which includes warring factions such as the Jacobin Jack-o-Bite franchise, the monarchist Food Court and the Whiggery Piggery.
