Writing style: additions, improvements

documentation/content/en/books/fdp-primer/writing-style/_index.adoc

@@ -168,7 +168,7 @@ For more information about writing style, see http://www.bartleby.com/141/[Eleme
 To keep the source for the documentation consistent when many different people are editing it, please follow these style conventions.
 
 [[one-sentence-per-line]]
-== One sentence per line
+=== One sentence per line
 
 Use Semantic Line Breaks in the documentation, a technique called "one sentence per line".
 The idea of this technique is to help the users to write and read documentation.
@@ -187,8 +187,34 @@ All human beings are born free and equal in dignity and rights.
 They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.
 ....
 
+[[sentence-spacing]]
+=== Spaces between sentences
+
+There are two conventions.
+
+*Generally*: 
+
+* one space. 
+
+This generalization includes monospaced representation of monospaced texts that do _not_ follow the two spaces convention.
+
+Where a variable-width font will be used: the per-line convention, above, will usually negate the need to think about spacing. 
+
+If a multi-sentence list item does use a space between sentences (with the possibility of strictly replacing the space with a line break): 
+
+* consider edition, to have no more than one sentence per point
+** do not assume that nesting of points is the solution
+** instead, an adjacent bullet point might be promoted to a simple paragraph.
+
+*Exceptionally*: 
+
+* two spaces in errata notices
+* two spaces in security advisories
+* two spaces in manual pages (in the `src` tree, for example)
+* two spaces in other files that will normally be viewed with a monospaced font.
+
 [[writing-style-acronyms]]
-== Acronyms
+=== Acronyms
 
 Acronyms should be defined the first time they appear in a document, as in: "Network Time Protocol (NTP)".
 After the acronym has been defined, use the acronym alone unless it makes more sense contextually to use the whole term.