Add float vs discrete heading usage instruction

src/docs/asciidoc/en/firebirddocs/docwritehowto/firebird-docwriting-guide.adoc

@@ -771,6 +771,32 @@ or
 
 The second syntax offers more flexibility when you need to provide more options and attributes than just the ID.
 
+[[docwritehowto-asciidoc-float-heading]]
+==== Float vs discrete headings
+
+AsciiDoctor allows you to define headings that are not part of the document outline (eg the TOC).
+See also https://asciidoctor.org/docs/user-manual/#discrete-headings[Discrete Headings (aka Floating Titles)^].
+AsciiDoctor offers two roles to do this: `float` and `discrete`:
+
+[source]
+----
+[float]
+== Section heading with float
+
+[discrete]
+== Section heading with discrete
+----
+
+In the HTML output we generate the TOC dynamically using tocbot.
+Unfortunately, tocbot allows us to only exclude a single class from the selection of headings.
+To avoid the introduction of a separate custom role, we chose `float` as the role to use for these types of elements.
+Do not use the `discrete` role to prevent it from showing up in the HTML TOC generated by tocbot.
+
+[NOTE]
+====
+We decided on `float` instead of `discrete` based on the fact that we were already using `float`.
+====
+
 [[docwritehowto-asciidoc-customrole]]
 ==== Custom roles