Apply suggestions from code review

Co-authored-by: David Allsopp <david.allsopp@metastack.com>

doc/pages/Manual.md

@@ -52,8 +52,8 @@ following hierarchy:
   they override what may already be present in the `opam` file
 - [`/packages/<pkgname>/<pkgname>.<version>/files/`](#files): contains files
   that are copied over the root of the source tree of the given package before
-  it gets used. Before opam 2.2 every files in this directory were copied but
-  since opam 2.3 only the files listed in the
+  it gets used. Before opam 2.3, all files in this directory were copied. 
+  Since opam 2.3 _only_ the files listed in the
   [`extra-files`](#opamfield-extra-files) field are copied.
 - `/cache/`: cached package files, by checksum. Note that the cache location is
   configured in the [repo](#repofield-archive-mirrors) file, this name is only
@@ -1219,9 +1219,9 @@ files.
 
 - <a id="opamfield-extra-files">`extra-files: [ [ <string> <checksum> ] ... ]`</a>:
   lists the files below `files/` with their checksums. Used
-  internally for integrity verifications. Before opam 2.3, this field was
-  optional, since opam 2.3 this field is now mendatory when wanting to
-  copy files from the `files/` directory.
+  internally for integrity verification. Before opam 2.3, listing files in
+  this field was optional, but since opam 2.3 all files must be listed in
+  this field or they will not be copied from the `files/` directory.
 
 - <a id="opamfield-pin-depends">`pin-depends: [ [ <package> <URL> ] ... ]`</a>:
   this field has no effect on the package repository, but is useful for
@@ -1298,9 +1298,10 @@ will be copied over the root of the package source. If already present, files
 are overwritten, and directories are recursively merged. [`opam`](#opam) file
 fields like [`patches:`](#opamfield-patches) refer to files at that same root,
 so patches specific to opam are typically included in
-this subdirectory. Since opam 2.3, the [`extra-files:`](#opamfield-extra-files)
-must be list each files in this directory. Before opam 2.3 this field was
-optional.
+this subdirectory. Since opam 2.3, files must be listed in the
+[`extra-files:`](#opamfield-extra-files) or they are ignored. Before
+opam 2.3, all files were copied regardless of whether they appeared
+in the `extra-files` list.
 
 Also see the [`extra-sources:`](#opamsection-extra-sources) opam section, which has
 a similar behaviour and is processed before the `files/` are copied.