Explainer
What Is a FOSI?
The Short Answer
The Style Half of an SGML Manual
In the SGML era, defense technical manuals were tagged against a DTD, and the tags carried no appearance. The appearance lived in a second file, the FOSI. MIL-M-28001 defines it as an instance of the Output Specification (OS) that assigns values to the style characteristics for one particular DTD, written in the syntax of an SGML document instance. The Output Specification itself is written in DTD syntax.
If you own legacy Army or other DoD manuals in SGML, the FOSI is the other half of the delivery. It is also the half most often lost, because teams archive the content and forget the file that decides what a page looks like. For the markup itself, see what SGML is and the SGML standard page.
How It Works
Three Pieces, One Page
- The DTD says what the content is
- Elements, order, and nesting. A manual that validates against the DTD is structurally correct, and says nothing about how it looks.
- The FOSI says how it looks
- Values for fonts, spacing, page layout, numbering, and the rest of the formatting characteristics, assigned to the DTD's elements and to the contexts in which they appear.
- The formatter joins them
- A composition system reads the tagged source and the FOSI together and produces the page. The standard's goal was that different systems would produce the same intended result from the same pair.
The standard is firm about the pairing. A DTD interprets the content and structure of a functional specification such as MIL-M-38784, and a FOSI interprets its style and formatting. A FOSI delivered with a document must carry values for every significant tag and for every context where a tag has a unique formatting requirement. Where a contract wanted a variant, the standard required an unambiguous FOSI for it.
The Standard
MIL-M-28001 and MIL-PRF-28001
The specification is titled Markup Requirements and Generic Style Specification. MIL-M-28001B is dated 26 June 1993 and superseded A of 20 July 1990. It was later reissued as a performance specification, MIL-PRF-28001C, dated 2 May 1997. A notice dated 22 April 2010 marks C as inactive for new design and says it shall no longer be used as a guidance reference for new designs. The listings we used for the notice are secondary, so confirm the current status in ASSIST before you cite it in a bid.
Inactive for new design does not mean the files vanished. It means no new program should adopt the scheme, while contracts and libraries built under it keep their FOSIs. That is exactly the situation a conversion program meets.
Army Context
FOSIs and the 40051 Lineage
The Army manual family grew up on this model: a government DTD for the content standard, and a government FOSI for the look. AMCOM Publication Services in Redstone still publishes the MIL-STD-40051 DTDs, FOSIs, and Production Business Rules together. Our guides explain the layers a bid has to price in IADS in an Army RFP, and the constraints that matter when you author in authoring for IADS.
Revision E of MIL-STD-40051 (25 March 2025) replaced the separate -1D and -2D parts, so older contracts may cite revisions that no longer exist as separate documents. To place a manual in its generation, see Army technical manual numbering and which MIL-STD applies to a technical manual.
Why It Matters
Valid Is Not the Same as Right
A converted manual can pass every structural check and still be rejected for how it looks, because content conformance and format conformance are separate tests. The FOSI is the evidence of what the old format was. It records the numbering, the generated text, the page furniture, and the table treatments that the content never states.
The modern equivalent is the stylesheet layer. In general XML publishing it is XSLT feeding a formatter through XSL-FO, or CSS; our guide to how XML becomes a PDF walks through it. On an Army program, ask which stylesheet set the customer expects, whether it is theirs or yours to supply, and which viewer renders the result.
In a Conversion
Practical Steps
- Get the FOSI that shipped with the legacy delivery, plus the DTD revision it was written against. They are a pair, and a FOSI for one revision may not fit another.
- Render a sample of real pages through the old pipeline and keep the output. That is your fidelity baseline, and it is better evidence than the manual's own style notes.
- Inventory what the FOSI does that the content does not say: generated text, numbering, table treatments, running heads, change markers. Each needs an owner in the new pipeline.
- Decide the target before you build style: IADS-delivered XML under the program's current rules, S1000D, or DITA. The target decides whether the FOSI is replaced by a government stylesheet, a program stylesheet, or a new one.
- Compare old and new pages side by side on the baseline sample, and agree in writing what counts as a difference worth fixing.
The structural side of the move is covered in SGML to S1000D conversion. Expect the FOSI to inform the style work, not to be translated mechanically.
FAQ
Questions We Hear
What does FOSI stand for?
Formatting Output Specification Instance. It is an instance of the Output Specification (OS), the SGML-based scheme in MIL-M-28001 for describing how a tagged document should be formatted.
Is a FOSI a stylesheet?
Yes, in the broad sense: it separates presentation from content. It is written in SGML syntax rather than in CSS or XSL, and it targets one specific DTD, so it is not portable to other structures.
Which standard defines the FOSI?
MIL-M-28001, later issued as the performance specification MIL-PRF-28001. The last revision found is C, dated 2 May 1997, and the listings we checked mark it inactive for new design since a 22 April 2010 notice. Existing programs and their documents still carry FOSIs.
Do I need a FOSI to convert an SGML manual to XML?
You need it to reproduce the old appearance accurately and to know what formatting the content relies on. You do not need to keep it: the new target gets its own stylesheet. Read the FOSI as a specification of the output, not as something to port line by line.
Does MIL-STD-40051 still use FOSIs?
AMCOM Publication Services has published FOSIs alongside the 40051 DTDs. Whether your program's current contract still calls for one depends on the revision it cites, so confirm with the contract and AMCOM instead of assuming. Our guide to which MIL-STD applies explains how the revisions fit together.
Get In Touch
Find the FOSI Before You Convert
Send us a sample of your legacy SGML manuals and the files that came with them. We will identify the DTD and FOSI pairing and tell you what the move involves.