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% \iffalse
%<*internal>
\begingroup
\input docstrip.tex
\keepsilent
\preamble
  ______________________________________________________
  The canoniclayout package for LaTeX
  Copyright (C) 2010-2020 Claudio Beccari 
  All rights reserved

  License information appended

\endpreamble

\postamble
Distributable under the LaTeX Project Public License,
version 1.3c or higher (your choice). The latest version of
this license is at: http://www.latex-project.org/lppl.txt

This work consists of this file canoniclayout.dtx, a README.txt file
and the derived files canoniclayout.sty and canoniclayout.pdf.

This work is "maintained"

\endpostamble
\askforoverwritefalse
%
\generate{\file{canoniclayout.sty}{\from{canoniclayout.dtx}{package}}}
\generate{\file{README.txt}{\from{canoniclayout.dtx}{txt}}}
%
\def\tmpa{plain}
\ifx\tmpa\fmtname\endgroup\expandafter\bye\fi
\endgroup
%</internal>
% \fi
%
% \iffalse
%<*driver>
\ProvidesFile{canoniclayout.dtx}
%</driver>
%<package>\NeedsTeXFormat{LaTeX2e}[2009/01/01]
%<package>\ProvidesPackage{canoniclayout}%
%<txt>\ProvidesFile{README.txt}
%<*package,txt>
   [2020-04-09 v.0.5 Canonic layout circumscribed to a circle]
%</package,txt>
%<*driver>
\documentclass[a4paper]{ltxdoc}
\paperwidth=210mm\paperheight=297mm
\pdfpagewidth=\paperwidth \pdfpageheight=\paperheight
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{textcomp}
\usepackage{multicol}
\usepackage{amsmath,array,booktabs}
\usepackage{pict2e}[2019/06/01]%
\usepackage{color,xfp}
\usepackage{canoniclayout}
\hfuzz 10pt

\newcommand*\class[1]{\textsf{#1}}
\newcommand*\pack[1]{\textsf{#1}}
\newcommand*\prog[1]{\textsl{#1}}
\newcommand*\file[1]{\texttt{#1}}
\definecolor{grigio}{gray}{.85}

\makeatletter
%\newdimen\CLinnermargin % 258
%\newdimen\CLmm          % 262
%\newdimen\CLpagewidth   % 260
%\newdimen\Clowermargin  % 264
%\newdimen\CLvoffset     % 256
\edef\CLinnermargin{\fpeval{\oddsidemargin+1in}}
\edef\CLmm{\fpeval{1mm}}
\edef\CLpagewidth{\fpeval{\paperwidth}}
\edef\CLlowermargin{\fpeval{\paperheight-\topmargin-\headheight-(1in)-\headsep-\textheight}}
\edef\CLvoffset{\fpeval{\headheight+\topmargin+1in-\paperheight}}
\edef\CLpageheight{\fpeval{\paperheight}}
\def\cblayoutdestro{%
\begin{picture}(0,0)(\CLinnermargin,-\CLvoffset)
\put(0,0){\unitlength=\p@
\put(0,0){\framebox(\CLpagewidth,\CLpageheight){}}
\color{red}
\put(\CLinnermargin,\CLlowermargin){\makebox(0,0)[bl]{\color{grigio}\rule{\textwidth}{\textheight}}}
	\Line(0,\CLpageheight)(\CLpagewidth,0)
	\put(\fpeval{\CLpagewidth/2},\fpeval{\CLlowermargin+(\textheight)/2}){\circle{\CLpagewidth}}
}
\end{picture}}
\def\ps@title{\ps@plain
\def\@oddhead{\cblayoutdestro}
\let\@evenhead\@oddhead}
\allowdisplaybreaks
\begin{document}
\GetFileInfo{canoniclayout.dtx}
\title{Package \pack{canoniclayout}}
\author{Claudio Beccari}
\date{\centering Version number \fileversion; last revision \filedate.\\
 e-mail: \texttt{claudio dot beccari at gmail dot com}\par}
 \maketitle\thispagestyle{title}
 \DocInput{canoniclayout.dtx}
\end{document}
%</driver>
% \fi
%
% \CheckSum{128}
%\begin{abstract}
%\noindent
% This package is a small extension that allows to determine the page 
% parameters for a canonical layout where the text block is placed onto
% the page in such a way as: $(a)$ its diagonal coincides with the page
% relevant diagonal, and $(b)$ the circle inscribed within the text block
% is tangent to the page sides. The text block width to height ratio is
% kept equal to the page ratio, as well as  the inner to outer and the
% upper to lower margin ratios.
%
% The canonical layout determined by this package is laid down on this
% very page; of course the actual text block  fits the text block grid,
% because this documentation is typeset by means of the \texttt{ltxdoc}
% document class, that by itself would use other layout parameters, but
% that is has been arranged so as to invoke this very package. This
% allows you to immediately evaluate this traditional layout and see if
% it fits your requirements.
%\end{abstract}
%
% \begin{multicols}{2}
% \tableofcontents
% \end{multicols}
%
% \section{Introduction}
% As any user of the \class{memoir} class knows well, this class allows
% to customise the page layout virtually without any limitation; such
% limitations are connected mainly with the user inconsistent data that
% miss to specify necessary information or give unnecessary or conflicting
% information. Also other classes and/or packages allow the customised
% design of the page layout; some other classes, such as the standard
% ones, do not have any facility to customise the page geometry, unless
% the user invokes suitable packages, such as \pack{geometry} or
% \pack{tyeparea}, just to male a couple of well known examples.
% 
% Many packages exist in order to specify a named layout; this package
% \pack{canoniclayout} is another one that computes the page parameters
% to determine the horizontal and vertical dimensions of the margins
% and the text block. All other details shall be specified by the user,
% for example the dimensions of the stock paper, the trimming widths,
% and therefore the position of the page onto the stock paper; and so on.
% This package deals only with the trimmed page, not with the page and
% stock paper relationship.
%
% \paragraph{Warning} This package works well only with a modern
% installation of the \TeX\ system; in particular it uses the
% facilities of the \pack{xfp} package, that is an interface between
% the end user and the lower level language known as \LaTeX\,3 (L3 for
% short). This implies a \LaTeX kernel implementation dated  at least
% 2029-01-01, and a complete installation of the \TeX\ system. In
% particular the availability of the \pack{xfp} package is checked,
% and if the typesetting program cannot fetch it, is issues a message
% and interrupts loading this package. It is a clear message that your
% installation is obsolete; you might have your good reasons for not
% using a modern release of the \TeX\ system, but either you upgrade
% your installation or you cannot use this package.

%
% \begin{figure}
% \makebox[\textwidth]{\makebox[1.1\textwidth][r]{%
% \unitlength=0.0015\textwidth
% \let\ul\unitlength
%	\begin{picture}(184,320)(0,-20)
%	\put(0,0){\framebox(184,297){}}
%	\put(27,70){\makebox(0,0)[bl]{\color{grigio}\rule{113\ul}{184\ul}}}
%	\put(92,-20){\makebox(0,0)[t]{Golden number canonical layout}}
%	\color{red}
%	\put(92,162){\circle{184}}
%	\linethickness{.2pt}
%	\multiput(0,297)(1.98918918919,-3.21081081082){93}{\line(184,-297){1}}
%	\end{picture}%
% \hfill
%	\unitlength0.0015\textwidth
%	\let\ul\unitlength
%		\begin{picture}(210,330)(0,-20)
%		\put(0,0){\framebox(210,297){}}
%		\put(25,51){\makebox(0,0)[bl]{\color{grigio}\rule{149\ul}{210\ul}}}
%		\put(105,-35){\makebox(0,0)[b]{ISO canonical layout}}
%		\color{red}
%		\put(105,156){\circle{210}}
%		\multiput(0,297)(2.27027027027,-3.21081081082){93}{\line(210,-297){1}}
%		\end{picture}%
% \hfill
%   \unitlength0.001591\textwidth
%   \let\ul=\unitlength
%   \begin{picture}(220,330)(0,-20)
%   \put(0,0){\framebox(220,280){}}
%   \put(20.742,33.6){\makebox(0,0)[bl]{\color{grigio}\rule{172.86\ul}{220\ul}}}
%   \put(110,-35){\makebox(0,0)[b]{Letter paper canonical layout}}
%   \color{red}
%   \put(110,143.6){\circle{220}}
%		\multiput(0,280)(2.37837837838,-3.02702702703){93}{\line(220,-280){1}}
%   \end{picture}
% }}%
% \caption{A right page with the relevant diagonal, the text block and the
% canonical circle.
% In this figure it is important to notice the page proportions, not the
% scale; matter of fact the letter paper height is 17.6\,mm shorter than
% the A4 paper, but the drawings to the same height emphasise the relative
% proportions of the various page parts.}
% \label{fig:canoniclayout}
% \end{figure}
%
% Figure~\ref{fig:canoniclayout} depicts the situation described above;
% the grey rectangle represents the type block; the dotted page diagonal,
% as it can be seen, passes through the diagonal vertices of the type
% block; at the same time the circle is tangent to both the type block
% and the page contour.
%
% It must also be noticed, in the sketch on the left, that the page
% rectangle is a golden one; therefore also the type block is a golden
% rectangle; the inner to the outer margin ratio is the golden section
% value so as this same ratio exists between the upper and the lower
% margin. This canonical layout implies that the type block height is
% equal to the page width.
%
% Therefore this canonical layout is not suited when the page width
% is too small compared to the page height: with the golden
% section\footnote{Here we denote $\phi=1,618\dots$
% with the name of \emph{golden number}, and its reciprocal
% $\varphi=0,618\dots$ with the name of \emph{golden section}.} this
% ratio is 0.618, with the ISO paper shape, in the sketch on the center,
% this ratio is 0,707, and so on.
%
% But it is equally unsuitable with squarish pages, such as the sketch
% on the right where the page proportions conform with the USA letter
% paper size: the type block leaves little space for the margins, as
% it is evident from the properties of the canonical circle, which
% is tangent to the page lateral sides and to the type block horizontal
% sides; to the limit in a square page the type block is so large that
% there is no room for the margins.
%
% \section{The mathematics of the canonical layout}
% If one plays a little with the drawing of figure~\ref{fig:canoniclayout}
% and applies what has been described in the Introduction, may easily
% derive the following formulas:
%\begin{align}
%&\text{Page shape ratio:}       &    x&=b/h      \label{equ:1}  \\
%&\text{Inner margin:}           &    I&=bx(1-x)/(1+x)           \\
%&\text{External margin:}        &    E&=b(1-x)/(1+x)            \\
%&\text{Top margin:}             &    T&=hx(1-x)/(1+x)           \\
%&\text{Bottom margin:}          &    B&=h(1-x)/(1+x)            \\
%&\text{Text width:}             &    W&=xb                      \\
%&\text{Text height:}            &    H&=b                       \\
%&\text{Circle center abscissa:} &  C_x&=0.5b                    \\
%&\text{Circle center ordinate:} &  C_y&=h(1-x)/(1+x)+b/2        \\
%&\text{Circle radius:}          &    R&=0.5b    \label{equ:10}
%\end{align}
% whose results are summarised in table~\ref{tab:canoniclayout} for
% three common values of the shape factor and for the letter paper
% shape ratio.
%
%\begin{table}[!b]\centering^^A\let~\enspace
%^^A\hrule
%\caption{Canonical layout ratios referred to the base
% (or width, $b$) and the height ($h$) of the trimmed page.}
%\label{tab:canoniclayout}
%\bigskip
%\begin{tabular}{l@{\qquad}*4{>{$}c<{$}}}
%\toprule
%                            &\multicolumn4c{Canon}      \\
%\multicolumn1c{Shape ratio} & \phi:1 & 3:2    & \sqrt2:1 & 11:8.5\\
%\midrule
% Page shape ratio           &0,618~    &0,666~  &0,707~    &0,773~  \\
% Inner margin               &0,146b    &0,133b  &0,121b    &0,099b  \\
% External margin            &0,236b    &0,200b  &0,172b    &0,128b  \\
% Upper margin               &0,146h    &0,133h  &0,121h    &0,099h  \\
% Lower margin               &0,236h    &0,200h  &0,172h    &0,128h  \\
% Text block width           &  0,618b  &0,666b  &0,707b    &0,773b  \\
% Text block height          & b        & b      &   b      &b       \\
% Circle center abscissa     & b/2      & b/2    & b/2      &b/2     \\
% Circle center ordinate     & 0,545h   &0,533h  &0,526h    &0,515h  \\
% Circle radius              & b/2      & b/2    & b/2      &b/2     \\
%\bottomrule
%\end{tabular}
%\end{table}
%
% Actually the formulas~\ref{equ:1}–\ref{equ:10}, and their numerical
% evaluations reported in table~\ref{tab:canoniclayout}, are just for
% general information. The actual computations are performed by this
% package, either by means of the \class{memoir} built-in facilities
% or by explicit computations that exploit the \pack{xfp} functions.
% But it can be easily seen that as the trimmed page becomes more
% squarish, the page size ratio tends to one, ad the margins become
% smaller and smaller. Therefore it seems that this layout is better
% suited for intermediate page ratios, such as the ISO one or the
% common European book size of 170\,mm $\times$ 240\,mm with a ratio
% of 0,708.
%
% \section{Usage}
% This package is invoked as usual with:
%\begin{verbatim}
%   \usepackahe{canoniclayout}
%\end{verbatim}
% No options are necessary; but it is necessary to invoke the package
% only after the actual page dimensions are known, be they specified
% by an option passed to the class, such as, for example, \texttt{a4paper},
% or by means of a \texttt{page}\meta{size} specification, for example
% \texttt{pagebv} for calling the ISO B5 size.
% 
% At any convenient moment after calling this package, the trimming
% margins with respect to the stock paper may be computed and the
% layout rechecked and fixed for consistency.
%
% \section{Font normal size}
% At the same time if this page layout is chosen, the font normal size
% should be selected on the actual text block width; it is possible
% that the golden ratio type block, on a golden rectangle paper obtained
% by trimming  an ISO A4 stock paper, might be suitable with a 10\,pt
% normal font size (exactly 66 characters per line with 10pt Latin
% Modern fonts), while a full ISO A4 paper yields a type block that
% might be more suited for a 12pt normal font size (86 characters with
% 10pt Latin Modern fonts is too much). The computations might be left
% to the \class{memoir} class commands, but it's better the user
% is aware of this particular point.
% For his/her sake this package provides the command |\currentfontletters|
% (to be used only after |\begin{document}|, because specific font
% packages might be loaded after the page layout has been computed; in
% any case the command is “text producing”, therefore it can't be used
% while in the preamble!) that types out a sentence such as “The number
% of characters in one text line with the current font is $nn$”, where
% the $nn$ is the actual number printed out. If such number is much
% larger than the ideal Bringhurst range of $66\pm6$, it's wiser to
% chose a larger normal font size. 
% In any case the alternative command |\charactersperpage| types out
% the same information, the number of lines and the estimated number
% of characters per page. These commands are supposed to be useful
% while setting up the complete preliminary parameters for the page
% layout. 
%
% Just to have a comparison, table~\ref{tab:sizes} displays the number
% of characters in one text line for several fonts and for page sizes
% A4, A5, and B5. As you see, although that Bringhurst range comes form
% socio-psychological studies and therefore has a large standard deviation,
% It appears that for the larger papers only those fonts with wider
% lowercase letters are suitable for this canonical layout; with smaller
% paper sizes, quite understandably, more font collections are suited.
% This very document, typeset with this canonical layout on A4 paper
% with a Latin Modern 10\,pt font size, has long text lines that stress
% the readers eyes.
%
%\begin{table}
%\caption{Text line lengths measured in average number
% of characters in different fonts}\label{tab:sizes}
% \bigskip
% 
% \centering
% \let\b\bfseries \let\i\itshape\tabcolsep=5pt
% \makebox[\textwidth]{\small\begin{tabular}{l*9c}
% \toprule
% Font collection  & \multicolumn3c{A4 paper size}
%                                & \multicolumn3c{A5 paper size}
%                                &\multicolumn3c{B5 paper size}\\
%  &10\,pt &11\,pt &12\,pt &10\,pt &11\,pt &12\,pt &10\,pt &11\,pt &12\,pt\\
% \midrule
% Times eXtended  
%  & \i92  & \i84  & \i77  & \b64  & 59    & \i54  & \i77  & \b70  &  \b64\\
% Latin Modern  
%  & \i86  & \i79  &   73  & \b60  & \i55  & \i51  & \b72  & \b66  &  \b61\\
% Kepler Project 
%  & \i83  &   76  & \b69  &   58  & \i53  & \i48  & \b69  & \b63  &    58\\
% Palatino eXtended
%  & \i82  &   75  & \b69  &   58  & \i53  & \i48  & \b69  & \b63  &    57\\
% \bottomrule
% \end{tabular}}
%\end{table}
%
% It can be seen that the bold measures satisfy the Bringhurst rule
% with a number of characters in the range $66\pm6$; the measures
% typeset in medium series type are out of  the optimal Bringhurst
% range, but may be considered acceptable; the measures typeset in
% italics  are completely out of the interval $66\pm10$ and should
% not be considered acceptable. This means that the large A4 paper
% size may be best used with intrinsically large fonts such as the
% Palatino eXtended (package \pack{newpxtext}) and the Kepler Project
% (package  \pack{kpfonts}). With the smaller A5 paper size with 10\,pt
% size fonts the best ones are the Times eXtended (package
% \pack{newtxtext}), and the Latin Modern ones (package \pack{lmodern})
% but substantially all the examined fonts are acceptable, while with
% 12\,pt fonts none are acceptable.
%
% With an intermediate sized paper, such as a B5 ISO size, all the
% considered fonts are acceptable inside or just outside the optimal Bringhurst interval.
%
% Many books are trimmed to a size close the B5 paper size, therefore
% the page layout produced with this package is most useful with medium
% and smaller sizes (at least with ISO sizes).

% \section{Conclusion}
% I don't think this package should set also the header and footer
% distances, for example, or should set any specification for the page
% “decorations”, such as underlined headers, or over lined footers,
% or the size, font family, series and shape of the header and footer
% contents. These specifications are of course important, but have
% nothing to do with the relationship between the paper size, the
% page size and the type block size. 
%
% As a final remark it's worth noting that a single pass of
% \prog{pdflatex} on this \file{canoniclayout.dtx} file produces at the
% same time both the \file{canoniclayout.sty} package file and the
% documentation \file{canoniclayout.pdf} file, besides a \file{README.txt}
% required for uploading to the \textsc{ctan} archives. After running
% \prog{pdflatex} move \file{canoniclayout.sty} to a
% \file{tex/latex/canoniclayout/} folder and \file{canoniclayout.pdf}
% to a \file{doc/latex\discretionary{}{/}{/}canoniclayout/} one;
% if such folders don't exist, create them on your personal \TeX\ 
% tree. After moving these files and if you have a Mik\TeX\ installation,
% remember to refresh the file name data base.
%
%
% \StopEventually{} 
%
% \section{Documented code}
% The package preliminaries are already in place. We are going to make
% some computations in order to determine the page shape factor $x$;
% to this end we exploit the dimensional computing capabilities package
% \pack{xft}, that are already available in the most recent \LaTeX\ 
% kernel files; in facts, the \LaTeX\,3 (L3) language computing
% facilities have been available for several years, but the simple
% and efficient user interface package \pack{xfp} has been available
% since the 2018 autumn. If these facilities are not available, either
% because the \TeX\ distribution is a little too old, or because the
% real \prog{tex} typesetting engine, not \prog{pdftex}, is being used,
% then, this entire package contents is skipped and nothing is done,
% except issuing a suitable warning.
%\iffalse
%<*package>
%\fi
%    \begin{macrocode}
\IfFileExists{xfp.sty}{\RequirePackage{xfp}}{%
	\PackageError{canoniclayout}{\MessageBreak%
	The xfp package is not available\MessageBreak
	and this package cannot work without\MessageBreak}{
	Reading of this package is skipped\MessageBreak
	Expect a different layout form the canonical one\Messagebreak
	Update your TeX system installation!\expandafter\endinput}}
%    \end{macrocode}
%
% In order to have this layout work with the \class{memoir} class or
% with any other class we have to test the fact that this package
% has been loaded within the preamble of a \class{memoir} styled document;
% according to the result of this test we can exploit
% the \class{memoir} facilities for determining the page geometry,
% or we have to carry out the complete computations ourselves.
%    \begin{macrocode}
\@ifclassloaded{memoir}{%
%    \end{macrocode}
% Working with the \class{memoir} facilities, we can determine the page
% shape factor and we save it into the control sequence |\CLshape|.
%    \begin{macrocode}
\edef\CLshape{\fpeval{\paperwidth / \paperheight}}
\edef\CLinvshape{\fpeval{1/\CLshape}}
%    \end{macrocode}
% We then assign the text height, thanks to the fact that the canonical
% layout has the block height just as long as the page width, due to the
% circle property mentioned in the Introduction; in any case the
% formulas~\ref{equ:1}--\ref{equ:10} and table~\ref{tab:canoniclayout} confirm this property for any shape.
%    \begin{macrocode}
\textheight=\paperwidth
%    \end{macrocode}
%
% This done, we can use the internal \class{memoir} commands to determine
% the other layout dimensions.
%    \begin{macrocode}
\settypeblocksize{\textheight}{*}{\CLshape}
\setlrmargins{*}{*}{\CLinvshape}
\setulmargins{*}{*}{\CLinvshape}
\setmarginnotes{7pt}{\dimexpr \foremargin-3\marginparsep}{\onelineskip}

%    \end{macrocode}
%
% We now use the |\checkandfixthelayout| so that it adjusts the type
% block dimensions to an integer number of lines in the normal font and
% eventually prints the page parameters to the \file{.log} file.
%    \begin{macrocode}
\checkandfixthelayout
%    \end{macrocode}
%
% At this point we are finished with the computations if the
% \class{memoir} class is the active one, but we need to perform
% the complete calculations in case we are not working with the
% \class{memoir} class.
%    \begin{macrocode}
}{%
%    \end{macrocode}
% We start by defining the lengths registers that hold the real inner,
% outer and upper margins, without the one inch shift and without taking
% into consideration the headings and their spacings, that must be
% specified before calling this package.
%    \begin{macrocode}
\newlength\innermargin
\newlength\outermargin
\newlength\uppermargin
%    \end{macrocode}
% Then we use some macros where to store some constant values; 
% we compute them using  the rimmed page width and height; 
%    \begin{macrocode}
\edef\CLpageratio{\fpeval{\paperwidth/\paperheight}} % x
\edef\CLlargeratio{\fpeval{(1-\CLpageratio)/(1+\CLpageratio)}} % y
\edef\CLsmallratio{\fpeval{\CLpageratio*\CLlargeratio}} % z
%    \end{macrocode}
% We compute the type block dimensions:
%    \begin{macrocode}
\textheight\paperwidth 
\textwidth=\CLpageratio\textheight
%    \end{macrocode}
% We then compute the real margins between the page sides and the type block:
%    \begin{macrocode}
\innermargin=\CLsmallratio\paperwidth 
\outermargin=\CLlargeratio\paperwidth 
\uppermargin=\CLsmallratio\paperheight
%    \end{macrocode}
% But the typesetting engine does not use the net margins, due to the
% historical one inch shift of the original \TeX\ implementation and,
% for the upper margin, due to the fact that by default this layout
% implies the headings and the footers outside the type block. Since
% we have the real outer margin dimension, we compute
% the actual default marginal note measure:
%    \begin{macrocode}
\marginparwidth=\fpeval{0.8\outermargin-\marginparsep}pt
\evensidemargin=\fpeval{\outermargin -(1in)}pt
\oddsidemargin=\fpeval{\innermargin-(1in)}pt
\topmargin=\fpeval{\uppermargin-(1in)-\headheight-\headsep}pt
%    \end{macrocode}
% When using different classes from the \class{memoir} one, we adjust
% the type block dimensions so that the type block contains an integer
% number of lines; we use the normal size |\baselineskip| value and 
% compute the number of lines contained in the initial type block minus
% the first line standard height equal to |\topskip|; notice that the
% integer value expression is a rounded value,
% not a truncated one, therefore the actual type block height might get
% enlarged or reduced by a very little bit that will not be noticed with
% naked eye when one examines a typeset page; eventually we recompute the
% |\textheight| taking into account the height of the first line.
%    \begin{macrocode}
\normalfont\textheight=%
\fpeval{round((\textheight - \topskip)/\baselineskip, 0) * \baselineskip + \topskip}pt%
\normalbaselineskip\baselineskip
%    \end{macrocode}
% and we eventually close the second action depending on the use of the
% \class{memoir} class:
%    \begin{macrocode}
}% end of test on the class being used
%    \end{macrocode}
%
% Just for testing the number of characters in a line, the following
% macros are provided. A couple of variables  will be used |\CLaux|
% and |\CLabcwidth|; |\CLabcwidth| will hold the current lowercase
% alphabet length, while |\CLaux| will hold several values in succession.
% The scratch variable |\CLcharcount| will receive the final result to be
% printed out.
%
% Another service macro for the user's sake is |\charactersperpage|; this
% macro typesets the average number of characters per line, the numbers of
% lines per page, and eventually their product, a good estimate of the
% number of characters per page.
%
% Many text editors have facilities for counting a “compuscript”
% number of words and characters; with this further information the
% user may easily estimate the number of pages of his/her document;
% of course s/he must allow a certain allowance for the front and back
% matter pages, so that s/he can evaluate the total amount of signatures
% of the whole typeset document; of course, by typesetting it with
% \prog{(pdf)latex} s/he knows exactly the number of pages of the final
% document, but the typography shop generally wants to know a good
% estimate before the source \TeX\ files are finished.
%    \begin{macrocode}
\newlength\abc@width
\settowidth\abc@width{abcdefghijklmnopqrstuvwxyz}%
\edef\CLcharcount{\fpeval{round(\textwidth * 26 / \abc@width,0)}}
\newcommand*\currentfontletters{%
\par The number of characters in one text line with the current font is
    \CLcharcount.\par}
%    
\newcommand*\charactersperpage{%
\edef\CLlinesperpage{\fpeval{round(\textheight / \baselineskip,0)}}
\edef\CLcharsperpage{%
  \fpeval{\CLcharcount * \CLlinesperpage}}
\begin{quote} The average number of characters in one text line
    with the current font is \CLcharcount;
    this text block contains \CLlinesperpage\ lines;
    a rough estimate of the number of characters per page is
    \CLcharsperpage.\par
    This information may be useful to evaluate the total number
    of pages in a document.
\end{quote}}

%    \end{macrocode}
% Using these macros, we can type out the information relative to this
% specific documentation.
% \charactersperpage
%\iffalse
%</package>
%<*txt>
%\fi
% 
%    \begin{macrocode}
Canoniclayout is a small extension package that allows to design 
a canonic layout based on the great circle inscribed within the 
page and tangent to the horizontal sides of the type block rectangle. 
The margins reflect the trimmed page shape ratio, therefore the 
type block principal diagonal coincides with the corresponding 
page diagonal; this layout is especially good for ISO page shapes 
but it can be used with many other traditional book page shapes.

This new version is completely new, in the sense that its code 
calculations are performed by means of the 2018 xfp package 
facilities. For this reason it cannot be used with any TeX 
distribution preceding the year 2018 and updated by the end of 
that year; should this happen this very package aborts its own 
input while advising the user by means of an Error Message. 

This work is released under  the Latex Project Public Licence 
v.1.3c. The LPPL is distributed with any TeX system distribution 
and can be found also in any CTAN archive.

Claudio Beccari 2020
claudio dot beccari at gmail dot com
%    \end{macrocode}
%\iffalse
%</txt>
%\fi
% \Finale
% \endinput
%