Template:Citation Style documentation/registration

 Citations of online sources that require registration or a subscription are acceptable in Wikipedia as documented in Verifiability § Access to sources. As a courtesy to readers and other editors, editors should signal the access restrictions of the external links included in a citation.

Four access levels can be used:
 * access indicator for named identifiers:
 * Lock-green.svg : the source is free to read for anyone
 * access indicators for url-holding parameters:
 * Lock-gray-alt-2.svg : a free registration is required to access the source
 * Lock-gray-alt-2.svg : there are other constraints (such as a cap on daily views) to freely access this source
 * Lock-red-alt-2.svg : the source is only accessible via a paid subscription ("paywall")

As there are often multiple external links with different access levels in the same citation, these values are attributed to a particular external link.

Access indicators for url-holding parameters
Sources linked by url, article-url, chapter-url, contribution-url, entry-url, map-url, and section-url are presumed to be free-to-read. When they are not free-to-read, editors should mark those sources with the matching access-indicator parameter so that an appropriate icon is included in the rendered citation. Because the sources linked by these url-holding parameters are presumed to be free-to-read, they may not be marked as.

Access indicator for named identifiers
Links inserted by named identifiers are presumed to lie behind a paywall or registration barrier – exceptions listed below. When they are free-to-read, editors should mark those sources with the matching access-indicator parameter so that an appropriate icon is included in the rendered citation. Because the sources linked by these named-identifier parameters are not presumed to be free-to-read, they may not be marked as,  , or.

Some named-identifiers are always free-to-read. For those named-identifiers there are no access-indicator parameters, the access level is automatically indicated by the template. These named identifiers are:
 * arxiv
 * biorxiv
 * citeseerx
 * pmc
 * rfc
 * ssrn