XMLWF(1) XMLWF(1)
NAME
xmlwf - Determines if an XML document is well-formed
SYNOPSIS
xmlwf [OPTIONS] [FILE ...]
xmlwf -h
xmlwf -v
DESCRIPTION
xmlwf uses the Expat library to determine if an XML document is well-
formed. It is non-validating.
If you do not specify any files on the command-line, and you have a re-
cent version of xmlwf, the input file will be read from standard input.
WELL-FORMED DOCUMENTS
A well-formed document must adhere to the following rules:
• The file begins with an XML declaration. For instance, <?xml ver-
sion="1.0" standalone="yes"?>. NOTE: xmlwf does not currently check
for a valid XML declaration.
• Every start tag is either empty (<tag/>) or has a corresponding end
tag.
• There is exactly one root element. This element must contain all oth-
er elements in the document. Only comments, white space, and process-
ing instructions may come after the close of the root element.
• All elements nest properly.
• All attribute values are enclosed in quotes (either single or dou-
ble).
If the document has a DTD, and it strictly complies with that DTD, then
the document is also considered valid. xmlwf is a non-validating pars-
er -- it does not check the DTD. However, it does support external en-
tities (see the -x option).
OPTIONS
When an option includes an argument, you may specify the argument ei-
ther separately ("-d output") or concatenated with the option ("-dout-
put"). xmlwf supports both.
-a factor
Sets the maximum tolerated amplification factor for protection
against billion laughs attacks (default: 100.0). The amplifica-
tion factor is calculated as ..
amplification := (direct + indirect) / direct
.. while parsing, whereas <direct> is the number of bytes read
from the primary document in parsing and <indirect> is the num-
ber of bytes added by expanding entities and reading of external
DTD files, combined.
NOTE: If you ever need to increase this value for non-attack
payload, please file a bug report.
-b bytes
Sets the number of output bytes (including amplification) needed
to activate protection against billion laughs attacks (default:
8 MiB). This can be thought of as an "activation threshold".
NOTE: If you ever need to increase this value for non-attack
payload, please file a bug report.
-c If the input file is well-formed and xmlwf doesn't encounter any
errors, the input file is simply copied to the output directory
unchanged. This implies no namespaces (turns off -n) and re-
quires -d to specify an output directory.
-d output-dir
Specifies a directory to contain transformed representations of
the input files. By default, -d outputs a canonical representa-
tion (described below). You can select different output formats
using -c, -m and -N.
The output filenames will be exactly the same as the input file-
names or "STDIN" if the input is coming from standard input.
Therefore, you must be careful that the output file does not go
into the same directory as the input file. Otherwise, xmlwf will
delete the input file before it generates the output file (just
like running cat < file > file in most shells).
Two structurally equivalent XML documents have a byte-for-byte
identical canonical XML representation. Note that ignorable
white space is considered significant and is treated equivalent-
ly to data. More on canonical XML can be found at
http://www.jclark.com/xml/canonxml.html .
-e encoding
Specifies the character encoding for the document, overriding
any document encoding declaration. xmlwf supports four built-in
encodings: US-ASCII, UTF-8, UTF-16, and ISO-8859-1. Also see
the -w option.
-k When processing multiple files, xmlwf by default halts after the
the first file with an error. This tells xmlwf to report the
error but to keep processing. This can be useful, for example,
when testing a filter that converts many files to XML and you
want to quickly find out which conversions failed.
-m Outputs some strange sort of XML file that completely describes
the input file, including character positions. Requires -d to
specify an output file.
-n Turns on namespace processing. (describe namespaces) -c disables
namespaces.
-N Adds a doctype and notation declarations to canonical XML out-
put. This matches the example output used by the formal XML
test cases. Requires -d to specify an output file.
-p Tells xmlwf to process external DTDs and parameter entities.
Normally xmlwf never parses parameter entities. -p tells it to
always parse them. -p implies -x.
-r Normally xmlwf memory-maps the XML file before parsing; this can
result in faster parsing on many platforms. -r turns off memo-
ry-mapping and uses normal file IO calls instead. Of course,
memory-mapping is automatically turned off when reading from
standard input.
Use of memory-mapping can cause some platforms to report sub-
stantially higher memory usage for xmlwf, but this appears to be
a matter of the operating system reporting memory in a strange
way; there is not a leak in xmlwf.
-s Prints an error if the document is not standalone. A document
is standalone if it has no external subset and no references to
parameter entities.
-t Turns on timings. This tells Expat to parse the entire file, but
not perform any processing. This gives a fairly accurate idea
of the raw speed of Expat itself without client overhead. -t
turns off most of the output options (-d, -m, -c, ...).
-v Prints the version of the Expat library being used, including
some information on the compile-time configuration of the li-
brary, and then exits.
-w Enables support for Windows code pages. Normally, xmlwf will
throw an error if it runs across an encoding that it is not
equipped to handle itself. With -w, xmlwf will try to use a Win-
dows code page. See also -e.
-x Turns on parsing external entities.
Non-validating parsers are not required to resolve external en-
tities, or even expand entities at all. Expat always expands
internal entities (?), but external entity parsing must be en-
abled explicitly.
External entities are simply entities that obtain their data
from outside the XML file currently being parsed.
This is an example of an internal entity:
<!ENTITY vers '1.0.2'>
And here are some examples of external entities:
<!ENTITY header SYSTEM "header-&vers;.xml"> (parsed)
<!ENTITY logo SYSTEM "logo.png" PNG> (unparsed)
-- (Two hyphens.) Terminates the list of options. This is only
needed if a filename starts with a hyphen. For example:
xmlwf -- -myfile.xml
will run xmlwf on the file -myfile.xml.
Older versions of xmlwf do not support reading from standard input.
OUTPUT
xmlwf outputs nothing for files which are problem-free. If any input
file is not well-formed, or if the output for any input file cannot be
opened, xmlwf prints a single line describing the problem to standard
output.
If the -k option is not provided, xmlwf halts upon encountering a well-
formedness or output-file error. If -k is provided, xmlwf continues
processing the remaining input files, describing problems found with
any of them.
EXIT STATUS
For option -v or -h, xmlwf always exits with status code 0. For other
cases, the following exit status codes are returned:
0 The input files are well-formed and the output (if requested)
was written successfully.
1 An internal error occurred.
2 One or more input files were not well-formed or could not be
parsed.
3 If using the -d option, an error occurred opening an output
file.
4 There was a command-line argument error in how xmlwf was in-
voked.
BUGS
The errors should go to standard error, not standard output.
There should be a way to get -d to send its output to standard output
rather than forcing the user to send it to a file.
I have no idea why anyone would want to use the -d, -c, and -m options.
If someone could explain it to me, I'd like to add this information to
this manpage.
SEE ALSO
The Expat home page: https://libexpat.github.io/
The W3 XML 1.0 specification (fourth edition): https://www.w3.org/TR/2006/REC-xml-20060816/
Billion laughs attack: https://en.wikipedia.org/wiki/Billion_laughs_attack
AUTHOR
This manual page was originally written by Scott Bronson <bronson@rin-
spin.com> in December 2001 for the Debian GNU/Linux system (but may be
used by others). Permission is granted to copy, distribute and/or modi-
fy this document under the terms of the GNU Free Documentation License,
Version 1.1.
March 4, 2022 XMLWF(1)
Generated by dwww version 1.14 on Sun Apr 20 07:33:22 CEST 2025.