Typographically separating logical argument from explanation and example I am currently writing a master's dissertation. In this dissertation I have chosen to typographically separate logical argument, (Theorems, Proofs, and Definitions) from aids to understanding (Examples, Remarks and Asides). 
Basically, sections that are intended to be rigorous is written in normal font, and sections that are intended to help the reader understand what is being written, but are not fundamental  are written italicised. 
The intention is simple: One who is familiar with the area is likely only checking definitions  or theorems, and can focus on the normal text without hunting through a mountain of prose that they are already familiar with.
Someone who is new to the area, and who is not yet interested in the nitty-gritty details of a formal definition can focus on the italicised text, perhaps going back to the normal text later for something more concrete.
However my supervisor seems to think this is a bad idea, and has asked me to find precedents for this from well-known authors. Has anyone seen something like this before?
PS. When i say italicised, i actually mean only slanted. It's much easier to read than actually-italicised text. I could change the font to sans-serif for those sections.
 A: I think that separating formal argument from aids to understanding
is an excellent idea, and the usual way of doing it -- by an "end
of proof" symbol and extra space before the next paragraph -- is 
not maximally clear. Someone skimming the text will not immediately
know whether a random paragraph is part of a proof or part of a
commentary or motivational remarks.
However, italics are hard on the eyes, so you need some other device.
Perhaps ordinary font, but indented, and/or another font that is 
easier on the eyes, such as sans serif.
A: I've seen books where some chatty stuff was put into margins, but you need really wide margins (or really short chats) for that.  You certainly should have a "remark" environment, but I think the question is what it should do typographically.  You might consider indentation, horizontal lines before and after, or a vertical line in the margin.  
A: If you really want to cite an example then you could say that Jantzen does this in the introduction to some of his chapters in "Lectures on Quantum Groups"
Rather than making a typographical distinction, why not just create a 'Remark' environment for chatty sections?
