Кандидат на престол : из истории политических и культурных связей России и Швеции ХI-ХХ веков / Г.М. Коваленко. (OCLC #43227577)

MARC field 530 is a general note about the availability of additional physical or digital forms:

530 __ ǂa Also issued online.

More specific information goes into 776:

776 08 ǂi Online version: ǂa Kovalenko, G.M. (Gennadii
    ̆ Mikhaĭlovich). ǂt Kandidat na prestol. ǂd Sankt-Peterburg
    : Russko-baltiĭskiĭ informat︠s︡ionnyĭ t︠s︡entr BLIT︠S︡, 1999 ǂw 

Currently, MARC records in OCLC are created at the manifestation level, and this method can be used to link together different manifestations of the same expression.


Witchcraft / by Charles Alva Hoyt ; [edited by Beatrice R. Moore]. (OCLC #6862966)

This expression exists in two manifestations: the print volume we had in hand, and an electronic version at Google Books and HathiTrust (search only).

In MARC, the link between manifestations is recorded in the “additional physical form” field, 776:

776 08 ǂi Online version: ǂa Hoyt, Charles Alva. ǂt Witchcraft.
  ǂd Carbondale : Southern Illinois University Press, ©1981
  ǂw (OCoLC)608095693

Laboratory evaluations of stabilized flue gas desulfurization sludge (scrubber sludge) and aggregate mixtures / by Mark Anderson, Gary W. Sharpe, David L. Allen, Herbert F. Southgate and Robert C. Deen. (OCLC #884361903)

When I first started cataloging ebooks, the standard was to catalog them as electronic reproductions of print, and with a separate record for each platform that provided the title. This made some sense, but was frustrating for copy cataloging when you’d see only a skimpy record for the copy you had access to, but a robust popular record for the copy from another vendor.

In 2009, the preferred standard changed to provider-neutral records; that is, all copies of a particular ebook should now be cataloged on a single record with 856 fields for each link that provides access to it. Fields in this record describe an electronic resource (rather than mainly describing print, with reproduction notes in a 533) and do not include details that only apply to specific platforms, such as added entries for the distributor or 506 notes describing restrictions on access. Such details can be added to local catalogs if they are helpful to patrons.

Since a single provider-neutral record can be used for manifestations with various carriers (PDF, HTML, plain text) but not all carriers (excludes print, microform), the level of cataloging is somewhere between expression and manifestation.