Within the *Corpus Iuris Canonici*, the Liber Extra section represents one of the main reference corpora for the consultation of papal decretals. The platform allows users to perform textual searches, apply dynamic filters, and view results enriched with comments and glosses. The general functioning mirrors that of the *Decretum Gratiani*, but includes additional features specifically dedicated to the Glossa Ordinaria.

From the homepage, by selecting Liber Extra as the reference corpus, the relevant search fields are activated. The user can:

• Enter a keyword in the Free text search field;
• Restrict the search to a specific book using the Select Book menu;
• Start the search using Search or reset the fields using Reset.

Filters are loaded dynamically and expand according to the selection of structural levels (e.g. book → chapter → paragraph).

Once the search is launched, the relevant results are displayed. Each entry contains:

• A clickable title to open the text detail;
• A content excerpt with highlighted keywords;
• The total number of results found.

If no matches are found, the message “No results found” is displayed.

By clicking on a result, the user accesses the text detail page, which displays:

• The title and the author (for example, *GREGORIUS*);
• The full body of the selected text;
• The Notes and Export buttons in the upper right corner;
• A guiding message for interacting with the text:

“Select some text to add notes, view cross-references or suggest corrections.”

From this page, users can read, annotate, or export the content in the same way as with other corpora.

A distinctive feature of the Liber Extra is the ability to consult the Glossa Ordinaria, an apparatus of canonical commentaries presented in parallel with the main text. When the user clicks on a portion of text highlighted in blue, a right-hand sidebar appears containing:

• The title of the gloss (e.g. *Cupiditas*);
• The associated explanatory or interpretative text;
• Any references to related sections or chapters.

This mode enables parallel navigation between the normative text and its commentary, facilitating philological analysis and comparison.

For further details on the functionality of the Notes button, please refer to the section *Notes and annotations management*.

For further details on the functionality of the Export button, please refer to the section *Export button*.

The Liber Extra section maintains the same graphical and functional consistency as the rest of the platform:

• Top tabs for quickly switching between corpora (*Corpus Iuris Canonici* / *Babylonian Talmud*);
• Session button (Access / Logout);
• Institutional footer with links to *About*, *Resources*, *Support*, *FAQ*, *Forum*, *Helpdesk*, and the official ITSERR project logos.