A round of clean-up/clarifications (#195)

* Capitalise TAP consistently
* Clarify that mirrors are optional
* Bump Date and VERSION after edits
* Apply suggestions from code review
* Note consistent snapshot requirements in "3.1. Repository layout"
  Briefly describe the requirement for unique identification of files for
  consistent snapshots and cross-link to "6.2. Consistent snapshots" for
  more information.

Signed-off-by: Joshua Lock <[email protected]>
Co-authored-by: lukpueh <[email protected]>

Author: joshuagl

tuf-spec.md

@@ -3,7 +3,7 @@ Title: The Update Framework Specification
 Shortname: TUF
 Status: LS
 Abstract: A framework for securing software update systems.
-Date: 2021-09-21
+Date: 2021-12-14
 Editor: Justin Cappos, NYU
 Editor: Trishank Karthik Kuppusamy, Datadog
 Editor: Joshua Lock, VMware
@@ -16,7 +16,7 @@ Boilerplate: copyright no, conformance no
 Local Boilerplate: header yes
 Markup Shorthands: css no, markdown yes
 Metadata Include: This version off, Abstract off
-Text Macro: VERSION 1.0.26
+Text Macro: VERSION 1.0.27
 </pre>
 
 Note: We strive to make the specification easy to implement, so if you come
@@ -216,13 +216,13 @@ when a client is unable to update.
 
 ### TUF Augmentation Proposal (TAP) support ### {#tuf-augmentation-proposal-tap-support}
 
-This major version (1.x.y) of the specification adheres to the following TAPS:
+This major version (1.x.y) of the specification adheres to the following TAPs:
 
 - [TAP 6](https://github.com/theupdateframework/taps/blob/master/tap6.md):
     Include specification version in metadata
 - [TAP 9](https://github.com/theupdateframework/taps/blob/master/tap9.md):
     Mandatory Metadata signing schemes
-- [Tap 10](https://github.com/theupdateframework/taps/blob/master/tap10.md):
+- [TAP 10](https://github.com/theupdateframework/taps/blob/master/tap10.md):
     Remove native support for compressed metadata
 - [TAP 11](https://github.com/theupdateframework/taps/blob/master/tap11.md):
     Using POUFs for Interoperability
@@ -399,7 +399,7 @@ publicly available in the [TAP directory](https://github.com/theupdateframework/
 
 An application uses the framework to interact with one or more repositories.
 A repository is a conceptual source of target files of interest to the
-application.  Each repository has one or more mirrors which are the actual
+application.  Each repository MAY have one or more mirrors as the
 providers of files to be downloaded.  For example, each mirror may specify a
 different host where files can be downloaded from over HTTP.
 
@@ -430,6 +430,13 @@ a repository are not specified by the framework.  The names of these files
 and directories are completely at the discretion of the application using
 the framework.
 
+However, when <a>CONSISTENT_SNAPSHOT</a>s are in use, there is a RECOMMENDED
+mechanism for naming target files on the repository (see
+[[#consistent-snapshots]]). If an application using the framework does not
+follow these recommendations, but wishes to support self-contained consistent
+snapshots the application MUST ensure that target files are persisted in a way
+where each target file can be uniquely and consistently addressed.
+
 ### Metadata files ### {#metadata-files}
 
 The filenames and directory structure of repository metadata are strictly