Thanks for your question and for including an example and the details of your mapping rule; very helpful.
The IPTC 2:80 By-line field is defined in the IPTC specification as folloes:
2:80 By-line Repeatable, maximum 32 octets, consisting of graphic characters
plus spaces. Contains name of the creator of the objectdata, e.g. writer, photographer
or graphic artist. Examples:
“Robert Capa”
“Ernest Hemingway”
“Pablo Picasso”
The specification defines “Repeatable” values as follows:
Section 1.4 A program encountering a DataSet with a repeated tag number should
assume that it is “more or another of the same”, e.g. as where a sequence of subfiles
(or sub-images) is encountered. If a repeated tag number is encountered for a
DataSet defined as non-repeatable, an error condition is assumed and handled
without aborting the program and without aborting data capture, i.e. the data of the
first-encountered DataSet should be retained. The maximum number of repeats is not
defined. Where DataSets are repeatable, only one piece of data should be included in
that DataSet. For example, a DataSet defining news categories should include one
category per DataSet.
So, the proper way to include multiple By-line values is to have multiple, separate instances of the 2:80 dataset in the metadata, each containing one value for the field. The PHP iptcparse() function MLA uses to extract the metadata converts these to an array. There is no logic in the PHP function or in MLA to convert multiple, comma separated values in a single instance of the field to an array. The “Commas” format entry in the mapping rule is used to add commas to large numeric values in the custom field output. It does not have any effect on how the input value(s) are parsed.
Entering multiple values in repeatable fields depends on the tool you are using to embed the metadata.
I regret the news is not better, but I am marking this topic resolved simply because your question has been answered. Please post an update if you have further questions regarding the above explanation. Thanks for your interest in the plugin.
Thank you very much for the detailed and clear explanation @dglingren !!
Could you please share a link to the EXIF specification doc you’re referencing, as ideally I could find another attribute to re-purpose. I looked but can’t seem to find the exact one you shared.
Thank you!
The by-line field you are using is part of the IPTC standard, not the EXIF standard. The document I excerpted is this one: IIMV4.2.pdf (iptc.org). This page is also useful: IPTC Photo Metadata Standard 2023.2.
You can view and/or download this PDF document with more information: Mapping File Metadata to WordPress Fields with Media Library Assistant. The introduction includes many links to other resources. Also, the “Prefix values” subsection of the “Field-level Substitution Parameters” section in the Settings/Media Library Assistant Documentation tab has links to various standards documents.
