# Chapter 3 - Command-Line Reference

This chapter describes all of the command-line options supported by HTMLDOC.

## Basic Usage

The basic command-line usage for HTMLDOC is:

    % htmldoc options filename1.html ... filenameN.md ENTER
    % htmldoc options filename.book ENTER

The first form converts the named HTML or Markdown files to the specified output format immediately. The second form loads the specified `.book` file and displays the HTMLDOC window, allowing a user to make changes and/or generate the document interactively.

If no output file or directory is specified, then all output is sent to the standard output file.

On return, HTMLDOC returns an exit code of 0 if it was successful and non-zero if there were errors.

## Options

The following command-line options are recognized by HTMLDOC.

### -d directory

The `-d` option specifies an output directory for the document files.

This option is not compatible with the EPUB or PDF output formats.

### -f filename

The `-f` option specifies an output file for the document.

### -t format

The `-t` option specifies the output format for the document and can be one of the following:

Format | Description
--- | ---
epub | Generate an EPUB file.
html | Generate one or more indexed HTML files.
htmlsep | Generate separate HTML files for each heading in the table-of-contents.
pdf | Generate a PDF file (default version - 1.4).
pdf11 | Generate a PDF 1.1 file for Acrobat Reader 2.0 and later.
pdf12 | Generate a PDF 1.2 file for Acrobat Reader 3.0 and later.
pdf13 | Generate a PDF 1.3 file for Acrobat Reader 4.0 and later.
pdf14 | Generate a PDF 1.4 file for Acrobat Reader 5.0 and later.
ps | Generate one or more PostScript files (default level - 2).
ps1 | Generate one or more Level 1 PostScript files.
ps2 | Generate one or more Level 2 PostScript files.
ps3 | Generate one or more Level 3 PostScript files.

### -v

The `-v` option specifies that progress information should be sent/displayed to the standard error file.

### --batch filename.book

The `--batch` option specifies a book file that you would like to generate without the GUI popping up. This option can be combined with other options to generate the same book in different formats and sizes:

    % htmldoc --batch filename.book -f filename.ps ENTER
    % htmldoc --batch filename.book -f filename.pdf ENTER

### --bodycolor color

The `--bodycolor` option specifies the background color for all pages in the document. The color can be specified by a standard HTML color name or as a 6-digit hexadecimal number of the form `#RRGGBB`.

### --bodyfont typeface

The `--bodyfont` option specifies the default text font used for text in the document body. The `typeface` parameter can be one of the following:

typeface | Actual Font
--- | ---
Arial | Helvetica
Courier | Courier
Helvetica | Helvetica
Monospace | DejaVu Sans Mono
Sans | DevaVu Sans
Serif | DejaVu Serif
Times | Times

### --bodyimage filename

The `--bodyimage` option specifies the background image for all pages in the document. The supported formats are GIF, JPEG, and PNG.

### --book

The `--book` option specifies that the input files comprise a book with chapters and headings.

### --bottom margin

The `--bottom` option specifies the bottom margin. The default units are points (1 point = 1/72nd inch); the suffixes "in", "cm", and "mm" specify inches, centimeters, and millimeters, respectively.

This option is only available when generating PostScript or PDF files.

### --browserwidth pixels

The `--browserwidth` option specifies the browser width in pixels. The browser width is used to scale images and pixel measurements when generating PostScript and PDF files. It does not affect the font size of text.

The default browser width is 680 pixels which corresponds roughly to a 96 DPI display. Please note that your images and table sizes are equal to or smaller than the browser width, or your output will overlap or truncate in places.

### --charset charset

The `--charset` option specifies the 8-bit character set encoding to use for the entire document. HTMLDOC comes with the following character set files:

charset | Character Set
--- | ---
cp-874 | Windows code page 874
cp-1250 | Windows code page 1250
cp-1251 | Windows code page 1251
cp-1252 | Windows code page 1252
cp-1253 | Windows code page 1253
cp-1254 | Windows code page 1254
cp-1255 | Windows code page 1255
cp-1256 | Windows code page 1256
cp-1257 | Windows code page 1257
cp-1258 | Windows code page 1258
iso-8859-1 | ISO-8859-1
iso-8859-2 | ISO-8859-2
iso-8859-3 | ISO-8859-3
iso-8859-4 | ISO-8859-4
iso-8859-5 | ISO-8859-5
iso-8859-6 | ISO-8859-6
iso-8859-7 | ISO-8859-7
iso-8859-8 | ISO-8859-8
iso-8859-9 | ISO-8859-9
iso-8859-14 | ISO-8859-14
iso-8859-15 | ISO-8859-15
koi8-r | KOI8-R
utf-8 | UTF-8

> Note: UTF-8 support is limited to the first 128 Unicode characters found in the input.

### --color

The `--color` option specifies that color output is desired.

This option is only available when generating PostScript or PDF files.

### --compression[=level]

The `--compression` option specifies that Flate compression should be performed on the output file(s). The optional `level` parameter is a number from 1 (fastest and least amount of compression) to 9 (slowest and most amount of compression).

This option is only available when generating PDF or Level 3 PostScript files.

### --continuous

The `--continuous` option specifies that the input files comprise a web page (or site) and that no title page or table-of-contents should be generated. Unlike the `--webpage` option described later in this chapter, page breaks are not inserted between each input file.

This option is only available when generating PostScript or PDF files.

### --cookies 'name=\"value with space\"; name=value'

The `--cookies` option specifies one or more HTTP cookies that should be sent when converting remote URLs. Each cookie must be separated from the others by a semicolon and a space, and values containing whitespace or the semicolon must be placed inside double-quotes. When specifying multiple cookies, the entire cookie string must be surrounded by single quotes in order for the string to be processed correctly.

### --datadir directory

The `--datadir` option specifies the location of data files used by HTMLDOC.

### --duplex

The `--duplex` option specifies that the output should be formatted for two sided printing.

This option is only available when generating PostScript or PDF files. Use the `--pscommands` option to generate PostScript duplex mode commands.

### --effectduration seconds

The `--effectduration` option specifies the duration of a page transition effect in seconds.

This option is only available when generating PDF files.

### --embedfonts

The `--embedfonts` option specifies that fonts should be embedded in PostScript and PDF output. This is especially useful when generating documents in character sets other than ISO-8859-1.

### --encryption

The `--encryption` option enables encryption and security features for PDF output.

This option is only available when generating PDF files.

### --firstpage page

The `--firstpage` option specifies the first page that will be displayed in a PDF file. The `page` parameter can be one of the following:

page | Description
--- | ---
p1 | The first page of the document.
toc | The first page of the table-of-contents.
c1 | The first page of chapter 1.

This option is only available when generating PDF files.

### --fontsize size

The `--fontsize` option specifies the base font size for the entire document in points (1 point = 1/72nd inch).

### --fontspacing spacing

The `--fontspacing` option specifies the line spacing for the entire document as a multiplier of the base font size. A `spacing` value of 1 makes each line of text the same height as the font.

### --footer lcr

The `--footer` option specifies the contents of the page footer. The `lcr` parameter is a three-character string representing the left, center, and right footer fields. Each character can be one of the following:

lcr | Description
--- | ---
. | A period indicates that the field should be blank.
: | A colon indicates that the field should contain the current and total number of pages in the chapter (n/N).
/ | A slash indicates that the field should contain the current and total number of pages (n/N).
1 | The number 1 indicates that the field should contain the current page number in decimal format (1, 2, 3, ...)
a | A lowercase "a" indicates that the field should contain the current page number using lowercase letters.
A | An uppercase "A" indicates that the field should contain the current page number using UPPERCASE letters.
c | A lowercase "c" indicates that the field should contain the current chapter title.
C | An uppercase "C" indicates that the field should contain the current chapter page number.
d | A lowercase "d" indicates that the field should contain the current date.
D | An uppercase "D" indicates that the field should contain the current date and time.
h | An "h" indicates that the field should contain the current heading.
i | A lowercase "i" indicates that the field should contain the current page number in lowercase roman numerals (i, ii, iii, ...)
I | An uppercase "I" indicates that the field should contain the current page number in uppercase roman numerals (I, II, III, ...)
l | A lowercase "l" indicates that the field should contain the logo image.
l | An uppercase "L" indicates that the field should contain the logo image as a letterhead (shown at full size).
t | A lowercase "t" indicates that the field should contain the document title.
T | An uppercase "T" indicates that the field should contain the current time.
u | A lowercase "u" indicates that the field should contain the current filename or URL.

Setting the footer to "`...`" disables the footer entirely.

### --format format

The `--format` option specifies the output format for the document and can be one of the following:

Format | Description
--- | ---
epub | Generate an EPUB file.
html | Generate one or more indexed HTML files.
htmlsep | Generate separate HTML files for each heading in the table-of-contents.
pdf | Generate a PDF file (default version - 1.4).
pdf11 | Generate a PDF 1.1 file for Acrobat Reader 2.0 and later.
pdf12 | Generate a PDF 1.2 file for Acrobat Reader 3.0 and later.
pdf13 | Generate a PDF 1.3 file for Acrobat Reader 4.0 and later.
pdf14 | Generate a PDF 1.4 file for Acrobat Reader 5.0 and later.
ps | Generate one or more PostScript files (default level - 2).
ps1 | Generate one or more Level 1 PostScript files.
ps2 | Generate one or more Level 2 PostScript files.
ps3 | Generate one or more Level 3 PostScript files.

### --gray

The `--gray` option specifies that grayscale output is desired.

This option is only available when generating PostScript or PDF files.

### --header lcr

The `--header` option specifies the contents of the page header. The `lcr` parameter is a three-character string representing the left, center, and right header fields. See the `--footer` option for the list of formatting characters.

Setting the header to "`...`" disables the header entirely.

### --header1 lcr

The `--header1` option specifies the contents of the page header for the first body/chapter page. The `lcr` parameter is a three-character string representing the left, center, and right header fields. See the `--footer` option for the list of formatting characters.

Setting the header to "`...`" disables the first page header entirely.

### --headfootfont font

The `--headfootfont` option specifies the font that is used for the header and footer text. The `font` parameter can be one of the following:

- Courier
- Courier-Bold
- Courier-Oblique
- Courier-BoldOblique
- Helvetica
- Helvetica-Bold
- Helvetica-Oblique
- Helvetica-BoldOblique
- Monospace
- Monospace-Bold
- Monospace-Oblique
- Monospace-BoldOblique
- Sans
- Sans-Bold
- Sans-Oblique
- Sans-BoldOblique
- Serif
- Serif-Roman
- Serif-Bold
- Serif-Italic
- Serif-BoldItalic
- Times
- Times-Roman
- Times-Bold
- Times-Italic
- Times-BoldItalic

This option is only available when generating PostScript or PDF files.

### --headfootsize size

The `--headfootsize` option sets the size of the header and footer text in points (1 point = 1/72nd inch).

This option is only available when generating PostScript or PDF files.

### --headingfont typeface

The `--headingfont` options sets the typeface that is used for headings in the document. The `typeface` parameter can be one of the following:

typeface | Actual Font
--- | ---
Arial | Helvetica
Courier | Courier
Helvetica | Helvetica
Monospace | DejaVu Sans Mono
Sans | DevaVu Sans
Serif | DejaVu Serif
Times | Times

### --help

The `--help` option displays all of the available options to the standard output file.

### --helpdir directory

The `--helpdir` option specifies the location of the on-line help files.

### --hfimageN filename

The `--hfimageN` option specifies an image to use in the header and/or footer, where N is a number from 1 to 10. The supported formats are GIF, JPEG, and PNG.

### --jpeg[=quality]

The `--jpeg` option enables JPEG compression of continuous-tone images. The optional `quality` parameter specifies the output quality from 0 (worst) to 100 (best).

This option is only available when generating PDF or Level 2 and Level 3 PostScript files.

### --landscape

The `--landscape` option specifies that the output should be in landscape orientation (long edge on top).

This option is only available when generating PostScript or PDF files.

### --left margin

The `--left` option specifies the left margin. The default units are points (1 point = 1/72nd inch); the suffixes "in", "cm", and "mm" specify inches, centimeters, and millimeters, respectively.

This option is only available when generating PostScript or PDF files.

### --letterhead filename

The `--letterhead` option specifies the letterhead image for the page headers and footers for PostScript and PDF files. The supported formats are GIF, JPEG, and PNG.

> Note: You need to use the `--header` and/or `--footer` options with the `L` parameter or use the corresponding HTML page comments to display the logo image in the header or footer.

### --linkcolor color

The `--linkcolor` option specifies the color of links in EPUB, HTML. and PDF output. The color can be specified by name or as a 6-digit hexadecimal number of the form `#RRGGBB`.

### --links

The `--links` option specifies that PDF output should contain hyperlinks.

### --linkstyle style

The `--linkstyle` option specifies the style of links in EPUB, HTML, and PDF output. The style can be "plain" for no decoration or "underline" to underline links.

### --logoimage filename

The `--logoimage` option specifies the logo image for the HTML navigation bar and page headers and footers for PostScript and PDF files. The supported formats are GIF, JPEG, and PNG.

> Note: You need to use the `--header` and/or `--footer` options with the `l` parameter or use the corresponding HTML page comments to display the logo image in the header or footer.

### --no-compression

The `--no-compression` option specifies that Flate compression should not be performed on the output files.

### --no-duplex

The `--no-duplex` option specifies that the output should be formatted for one sided printing.

This option is only available when generating PostScript or PDF files. Use the `--pscommands` option to generate PostScript duplex mode commands.

### --no-embedfonts

The `--no-embedfonts` option specifies that fonts should not be embedded in PostScript and PDF output.

### --no-encryption

The `--no-encryption` option specifies that no encryption/security features should be enabled in PDF output.

This option is only available when generating PDF files.

### --no-jpeg

The `--no-jpeg` option specifies that JPEG compression should not be performed on large images.

### --no-links

The `--no-links` option specifies that PDF output should not contain hyperlinks.

### --no-localfiles

The `--no-localfiles` option disables access to local files on the system. This option should be used when providing remote document conversion services.

### --no-numbered

The `--no-numbered` option specifies that headings should not be numbered.

### --no-pscommands

The `--no-pscommands` option specifies that PostScript device commands should not be written to the output files.

### --no-strict

The `--no-strict` option turns off strict HTML conformance checking.

### --no-title

The `--no-title` option specifies that the title page should not be generated.

### --no-toc

The `--no-toc` option specifies that the table-of-contents pages should not be generated.

### --no-xrxcomments

The `--no-xrxcomments` option specifies that Xerox PostScript job comments should not be written to the output files.

This option is only available when generating PostScript files.

### --numbered

The `--numbered` option specifies that headings should be numbered.

### --nup pages

The `--nup` option sets the number of pages that are placed on each output page. Valid values for the `pages` parameter are 1, 2, 4, 6, 9, and 16.

### --outdir directory

The `--outdir` option specifies an output directory for the document files.

This option is not compatible with the PDF output format.

### --outfile filename

The `--outfile` option specifies an output file for the document.

### --owner-password password

The `--owner-password` option specifies the owner password for a PDF file. If not specified or the empty string (""), a random password is generated.

This option is only available when generating PDF files.

### --pageduration seconds

The `--pageduration` option specifies the number of seconds that each page will be displayed in the document.

This option is only available when generating PDF files.

### --pageeffect effect

The `--pageeffect` option specifies the page effect to use in PDF files. The `effect` parameter can be one of the following:

effect | Description
--- | ---
none | No effect is generated.
bi | Box Inward
bo | Box Outward
d | Dissolve
gd | Glitter Down
gdr | Glitter Down and Right
gr | Glitter Right
hb | Horizontal Blinds
hsi | Horizontal Sweet Inward
hso | Horizontal Sweep Outward
vb | Vertical Blinds
vsi | Vertical Sweep Inward
vso | Vertical Sweep Outward
wd | Wipe Down
wl | Wipe Left
wr | Wipe Right
wu | Wipe Up

This option is only available when generating PDF files.

### --pagelayout layout

The `--pagelayout` option specifies the initial page layout in the PDF viewer. The `layout` parameter can be one of the following:

layout | Description
--- | ---
single | A single page is displayed.
one | A single column is displayed.
twoleft | Two columns are displayed with the first page on the left.
tworight | Two columns are displayed with the first page on the right.

This option is only available when generating PDF files.

### --pagemode mode

The `--pagemode` option specifies the initial viewing mode in the PDF viewer. The `mode` parameter can be one of the following:

mode | Description
--- | ---
document | The document pages are displayed in a normal window.
outline | The document outline and pages are displayed.
fullscreen | The document pages are displayed on the entire screen in "slideshow" mode.

This option is only available when generating PDF files.

### --path dir1;dir2;dir3;...;dirN

The `--path` option specifies a search path for files that are loaded by HTMLDOC. It is usually used to get images that use absolute server paths to load.

Directories are separated by the semicolon (;) so that drive letters and URLs can be specified. Quotes around the directory parameter are optional. They are usually used when the directory string contains spaces.

    --path "dir1;dir2;dir3;...;dirN"

### --permissions permission[,permission,...]

The `--permissions` option specifies the document permissions. The available permission parameters are listed below:

Permission | Description
--- | ---
all | All permissions
annotate | User can annotate document
copy | User can copy text and images from document
modify | User can modify document
print | User can print document
no-annotate | User cannot annotate document
no-copy | User cannot copy text and images from document
no-modify | User cannot modify document
no-print | User cannot print document
none | No permissions

The `--encryption` option must be used in conjunction with the `--permissions` parameter.

    --permissions no-print --encryption

Multiple options can be specified by separating them with commas:

    --permissions no-print,no-copy --encryption

This option is only available when generating PDF files.

### --portrait

The `--portrait` option specifies that the output should be in portrait orientation (short edge on top).

This option is only available when generating PostScript or PDF files.

### --pdf-indent margin

The `--pdf-indent` option specifies the indentation for pre-formatted content. The default units are points (1 point = 1/72nd inch); the suffixes "in", "cm", and "mm" specify inches, centimeters, and millimeters, respectively.

### --pscommands

The `--pscommands` option specifies that PostScript device commands should be written to the output files.

This option is only available when generating Level 2 and Level 3 PostScript files.

### --quiet

The `--quiet` option prevents error messages from being sent to stderr.

### --referer url

The `--referer` option sets the URL that is passed in the `Referer:` field of HTTP requests.

### --right margin

The `--right` option specifies the right margin. The default units are points (1 point = 1/72nd inch); the suffixes "in", "cm", and "mm" specify inches, centimeters, and millimeters, respectively.

This option is only available when generating PostScript or PDF files.

### --size size

The `--size` option specifies the page size. The `size` parameter can be one of the following standard sizes:

size | Description
--- | ---
Letter | 8.5x11in (216x279mm)
A4 | 8.27x11.69in (210x297mm)
Universal | 8.27x11in (210x279mm)

Custom sizes are specified by the page width and length separated by the letter "x" to select a custom page size. Append the letters "in" for inches, "mm" for millimeters, or "cm" for centimeters.

This option is only available when generating PostScript or PDF files. Use the `--pscommands` option to generate PostScript page size commands.

### --strict

The `--strict` option turns on strict HTML conformance checking. When enabled, HTML elements that are improperly nested and dangling close elements will produce error messages.

### --textcolor color

The `--textcolor` option specifies the default text color for all pages in the document. The color can be specified by a standard HTML color name or as a 6-digit hexadecimal number of the form `#RRGGBB`.

### --textfont typeface

The `--textfont` options sets the typeface that is used for text in the document. The `typeface` parameter can be one of the following:

typeface | Actual Font
--- | ---
Arial | Helvetica
Courier | Courier
Helvetica | Helvetica
Monospace | DejaVu Sans Mono
Sans | DevaVu Sans
Serif | DejaVu Serif
Times | Times

### --title

The `--title` option specifies that a title page should be generated.

### --titlefile filename

The `--titlefile` option specifies a HTML or Markdown file to use for the title page.

### --titleimage filename

The `--titleimage` option specifies the title image for the title page. The supported formats are GIF, JPEG, and PNG.

### --tocfooter lcr

The `--tocfooter` option specifies the contents of the table-of-contents footer. The `lcr` parameter is a three-character string representing the left, center, and right footer fields. See the `--footer` option for the list of formatting characters.

Setting the TOC footer to "`...`" disables the TOC footer entirely.

### --tocheader lcr

The `--tocheader` option specifies the contents of the table-of-contents header. The `lcr` parameter is a three-character string representing the left, center, and right header fields. See the `--footer` option for the list of formatting characters.

Setting the TOC header to "`...`" disables the TOC header entirely.

### --toclevels levels

The `--toclevels` options specifies the number of heading levels to include in the table-of-contents pages. The `levels` parameter is a number from 1 to 6.

### --toctitle string

The `--toctitle` options specifies the string to display at the top of the table-of-contents; the default string is "Table of Contents".

### --top margin

The `--top` option specifies the top margin. The default units are points (1 point = 1/72nd inch); the suffixes "in", "cm", and "mm" specify inches, centimeters, and millimeters, respectively.

This option is only available when generating PostScript or PDF files.

### --user-password password

The `--user-password` option specifies the user password for a PDF file. If not specified or the empty string (""), no password will be required to view the document.

This option is only available when generating PDF files.

### --verbose

The `--verbose` option specifies that progress information should be sent/displayed to the standard error file.

### --version

The `--version` option displays the HTMLDOC version number.

### --webpage

The `--webpage` option specifies that the input files comprise a web page (or site) and that no title page or table-of-contents should be generated. HTMLDOC will insert a page break between each input file.

This option is only available when generating PostScript or PDF files.

### --xrxcomments

The `--xrxcomments` option specifies that Xerox PostScript job comments should be written to the output files.

This option is only available when generating PostScript files.

## Environment Variables

HTMLDOC looks for several environment variables which can override the default directories, display additional debugging information, and disable CGI mode.

### HTMLDOC_DATA

This environment variable specifies the location of HTMLDOC's data and fonts directories, normally /usr/share/htmldoc or C:\Program Files\HTMLDOC.

### HTMLDOC_DEBUG

This environment variable enables debugging information that is sent to stderr. The value is a list of keywords separated by spaces:

keyword | Information Shown
--- | ---
`links` | Shows all of the links in a document
`memory` | Shows memory usage statistics
`remotebytes` | Shows the number of bytes that were transferred via HTTP
`table` | Puts a box around each table, row, and cell
`tempfiles` | Shows the temporary files that were created, and preserves them for debugging
`timing` | Shows the load and render times
`all` | All of the above

### HTMLDOC_HELP

This environment variable specifies the location of HTMLDOC's documentation directory, normally /usr/share/doc/htmldoc or C:\Program Files\HTMLDOC\doc.

### HTMLDOC_NOCGI

This environment variable, when set (the value doesn't matter), disables CGI mode. It is most useful for using HTMLDOC on a web server from a scripting language or invocation from a program.

## Messages

HTMLDOC sends error and status messages to stderr unless the `--quiet` option is provided on the command-line. Applications can capture these messages to relay errors or statistics to the user.

### BYTES: Message

The `BYTES:` message specifies the number of bytes that were written to an output file. If the output is directed at a directory then multiple `BYTES:` messages will be sent.

### DEBUG: Messages

The `DEBUG:` messages contain debugging information based on the value of the `HTMLDOC_DEBUG` environment variable. Normally, no `DEBUG:` messages are sent by HTMLDOC.

### ERRnnn: Messages

The `ERRnnn:` messages specify an error condition. Error numbers 1 to 14 map to the following errors:

1. No files were found or loadable.
2. No pages were generated.
3. The document contains too many files or chapters.
4. HTMLDOC ran out of memory.
5. The specified file could not be found.
6. The comment contains a bad HTMLDOC formatting command.
7. The image file is not in a known format.
8. HTMLDOC was unable to remove a temporary file.
9. HTMLDOC had an unspecified internal error.
10. HTMLDOC encountered a networking error when retrieving a file via a URL.
11. HTMLDOC was unable to read a file.
12. HTMLDOC was unable to write a file.
13. A HTML error was found in a source file.
14. A table, image, or text fragment was too large to fit in the space provided.
15. A hyperlink in the source files was unresolved.
16. A header/footer string in the document contains a bad $ command.
17. The content is too nested to safely render.

Error numbers 100 to 505 correspond directly to a HTTP status code.

### INFO: Messages

The `INFO:` messages contain general information that is logged when HTMLDOC is running in CGI mode or when you use the `--verbose` option.

### PAGES: Message

The `PAGES:` message specifies the number of pages that were written to an output file. If the output is directed at a directory then multiple `PAGES:` messages will be sent. No `PAGES:` messages are sent when generating HTML or EPUB output.

### REMOTEBYTES: Message

The `REMOTEBYTES:` message specifies the number of bytes that were transferred using HTTP. This message is only displayed if the `HTMLDOC_DEBUG` environment variable has the keyword `remotebytes` or `all`.

### TIMING: Message

The `TIMING:` message specifies the load, render, and total time in seconds for the current command. This message is only displayed if the `HTMLDOC_DEBUG` environment variable has the keyword `timing` or `all`.