Help: CS1 errors

==<span id="bad_sbn">Check |sbn= value</span>==
<section begin="bad_sbn_help_text" />{{help desk}}{{#invoke:Cs1 documentation support|help_text_error_messages|err_bad_sbn|$1=&lt;type>}}

{{cs1}} and {{cs2}} templates that contain {{para|sbn}} are checked to ensure that the [[Standard Book Number|SBN]] is the proper length (nine digits), that the SBN uses the correct optional separators (simple space or hyphen), and that the final [[check digit]] is correct according to the SBN specification. Only one SBN is allowed in this field because the whole {{para|sbn}} value is included in the citation's [[COinS]] [[metadata]]. See also [[Wikipedia:COinS]]. More than one SBN, or characters that are not part of the SBN, corrupt the COinS metadata and may also corrupt the link to [[Special:BookSources]].

The error message &lt;type> indicator can be:
: <span class="error" style="font-size:100%">length</span> – SBN is not 9 digits
: <span class="error" style="font-size:100%">checksum</span> – SBN has one or more incorrect digits; look for typos and transposition
: <span class="error" style="font-size:100%">invalid character</span> – SBN has one or more 'digits' that is not in the allowed set
: <span class="error" style="font-size:100%">invalid form</span> – mis-positioned 'X' check digit

To resolve this error, ensure that the {{para|sbn}} value is correct, that only one SBN is used, that the proper optional separators are used, and that no other text is included. If the check digit is a lowercase 'x', change it to an uppercase 'X'.

* '''Do not''' try to resolve the error by simply recalculating the check digit.  The check digit is there to check whether the main part of the number is correct.  If the SBN is failing to validate, it is likely that there is a typo in the main part of the number.  In this case, recalculating the check digit results in an apparently valid ISBN that leads to the wrong source (or to nowhere).
* If the SBN as printed in your source is refusing to validate, '''do''' check both the front matter and the book cover for SBNs.  It is not uncommon for the SBN to be misprinted in the front matter but correct on the cover.
* '''Do''' preview your edit and check that the new SBN does now link to the correct source.

In very rare cases, publishers have released books with malformed SBNs. If you are certain that a non-conforming SBN truly corresponds to the published work, then you can add [[Help:Citation_Style_1#Accept-this-as-written_markup|accept-this-as-written markup]] around the identifier to suppress the error message. In many cases, books may have been reissued with a corrected SBN. Use a corrected SBN when possible.

Pages with this error are automatically placed in {{#invoke:cs1 documentation support|help_text_cats|err_bad_sbn|pages=yes}}.<ref group="lower-alpha" name="categories" /><section end="bad_sbn_help_text" />
Description	What you type	What you get
Italic	''Italic text''	Italic text
Bold	'''Bold text'''	Bold text
Bold & italic	'''''Bold & italic text'''''	*Bold & italic text*
Description	What you type	What you get
Reference	Page text.<ref>[https://www.example.org/ Link text], additional text.</ref>	Page text.^[1]
Named reference	Page text.<ref name="test">[https://www.example.org/ Link text]</ref>	Page text.^[2]
Additional use of the same reference	Page text.<ref name="test" />	Page text.^[2]
Display references	<references />	↑ Link text, additional text. ↑ Link text