An item's "seo" (MishkaCmsMigration.Sources.WordPress reads it from Yoast SEO and Rank Math) as the seo_tags a CMS page or a Blog post stores, for the targets that write them (MishkaCmsMigration.Targets.CmsPage, MishkaCmsMigration.Targets.BlogPost). Each tag is written as the core's head reads a stored tag (MishkaCmsCore.Runtime.Seo.stored_tag/3), and replaces the default the head would draw for it:

• "title" — the title; a {{page.title}} or {{site.name}} in it is the core's own variable;
• "description" — the description meta;
• "robots" — the robots meta, such as noindex, nofollow;
• "image" — the og:image meta: the Media address of the file the same run, or an earlier one, wrote for its "image_id" (MishkaCmsMigration.Targets.CmsMedia.addresses/2). An image on another site than the source keeps its address; one on the source that was not imported is left out, and so is the target's featured file: a page with no stored og:image gets the core's share card (MishkaCmsCore.Runtime.ShareCard), which draws a Blog post's featured image, and a stored one would replace that card;
• "canonical" — the canonical link. The source keeps only a canonical on another site;
• "og_title" and "og_description" — the og:title and og:description metas, the social title and description when they say something else than the title and the description;
• "twitter_title" and "twitter_description" — the twitter:title and twitter:description metas;
• "twitter_image" — the twitter:image meta, kept and left out by the same rules as "image" (its "twitter_image_id"), and left out too when it is the og:image the page stores, which the head already repeats for Twitter;
• "twitter_card" — the twitter:card meta, only summary: the head draws summary_large_image for a page with an image by itself.

The core's head stacks these over the layout's and a plugin's, a tag by its name and attributes, so each one replaces the default for that tag, and none is drawn twice.

A title and a description are stored as the item carries them, plain text, which the head escapes once: the source has already read the HTML entities its CMS answers (MishkaCmsMigration.Sources.WordPress).

An item without "seo" has no tags.