Help: CS1 errors

==<span id="bad_issn">Check |issn= value</span>==
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*{{#invoke:Cs1 documentation support|help_text_error_messages|err_bad_issn|$1=_}}
*{{#invoke:Cs1 documentation support|help_text_error_messages|err_bad_issn|$1=e}}
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{{cs1}} and {{cs2}} templates that contain {{para|issn}} and/or {{para|eissn}} are checked to ensure that the [[ISSN]] is the proper length (eight digits) and that the final [[check digit]] validates according to the ISSN specification. Only one each of ISSN and eISSN is allowed in this field because the whole {{para|issn}} and {{para|eissn}} values are included in the citation's [[COinS]] [[metadata]]. See also [[Wikipedia:COinS]]. (If relevant, they can be specified using {{para|id|{{tlp|ISSN|...}} {{tlp|EISSN|...}}}} instead.)

The ISSN and eISSN are always rendered as two four-digit numbers separated with a hyphen.

To resolve this error, ensure that the {{para|issn}} and {{para|eissn}} values are correct, that only one value per parameter is used, and that no other text is included (allowable characters are 0–9, X, and -). If the check-digit is a lowercase 'x', change it to an uppercase 'X'. It may also be worth checking an actual [[hyphen]] (-) has been used, and not a hyphen-like character like an [[endash]] (–).

In very rare cases, publishers have released works with a malformed identifier. If you are certain that a non-conforming identifier 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 some cases, works may have been reissued with a corrected identifier. Use the corrected one when possible.

Pages with this error are automatically placed in {{#invoke:cs1 documentation support|help_text_cats|err_bad_issn|pages=yes}}.<ref group="lower-alpha" name="categories" /><!-- See [[bugzilla:47049]] about {{FULLPAGENAME}}, category pagenames containing ISSN, and #ifeq: --><section end="bad_issn_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