One of the main disadvantages of the current state of Istrian source editing (ecdotics) is the fact that there is no single unifying set of editorial principles governing the editions of the sources. For example, the transcription principles of Vincenzo Joppi, the editor of some of the seminal sources for the history of medieval Istria, differ greatly from those of Antonio Stefano Minotto. Moreover, although working in the middle of the 19th century, the period in which scientific methods of source criticism were already established, Pietro Kandler relied on heavily outdated editorial principles; the historian from Trieste even took it upon himself to “correct” medieval authors by, for example, adding diphthongs to nouns and adjectives or even changing the tenses of verbs and their moods from indicative to subjunctive. From the present day's perspective, such editorial principles are atrocious and utterly unacceptable.
Therefore, one of the key goals of the project is not only to collect all the editions of the primary sources pertaining to medieval Istria in one place, but also to edit the transcriptions according to a single set of editorial principles according to contemporary lege artis.
Having consulted several seminal publications dedicated to editing medieval sources, such as Robert B. C. Huygens, Ars edendi: A Practical Introduction to Editing Medieval Latin Texts (Turnhout 2000), Jakov Stipišić, Pomoćne povijesne znanosti u teoriji i praksi [Auxiliary Sciences of History in Theory and Practice] (Zagreb 31991), Henry Ansgar Kelly, “Uniformity and Sense in Editing and Citing Medieval Texts,” Medieval Academy News 148 (Spring 2004): 8-9 and, most notably, Paolo Cammarosano, L'edizione dei documenti medievali: Una guida pratica (Trieste 2011), the editorial principles have been set out as following:
Every entry is given a unique signature, often (but not necessarily) consisting of a year plus two to three letters (e.g. 1210_OIV standing for the year 1210 and Emperor Otto IV). These entries are then chronologically sorted from the oldest to the youngest, from volume 1 to volume 6. The reason why the entries are not simply given a number, such as doc. 1 or doc. 78, lies in the fact that there are numerous unedited sources pertaining to the history of medieval Istria that will be systematically edited and entered into the database as part of the project. Therefore, adjacent entries today could in a matter of a year become quite distant from each other due to the editions of new, previously unknown sources. In order to avoid constantly having to renumber the documents every time new editions are published and introduced to the database, the current system of unique signatures is put in place, allowing for greater flexibility and consistency in citing the database entries.
After having been assigned its unique signature, every entry is then edited according to these fields:
- Era — gives the number of the chronologically ordered volume of the respective source edition, from vol. 1 to vol. 6.
- Series — classifies the entry in one of the several series of sources, of which the principal ones are
- Diplomata (for various acts of public and private nature such as imperial privileges, donations, etc.);
- Scriptores (for excerpts from various narrative sources such as chronicles or hagiographies);
- Leges (for legal sources such as statutes, ordinances, or tax rolls);
- Acta Veneta (for documents of Venetian constitutional bodies such as the Senate or the Great Council);
- Acta Patriarchalia (for the documents of the constitutional bodies of the Patriarchate of Aquileia such as the Friulian Parliament);
- Acta notariorum (for the entries featured in notarial books of imbreviatures);
- Acta potestatum (for the entries featured in the books of the rectors of Istrian communes);
- Regesta (for the entries featured in historical collections of regesta such as the famed Thesauri claritas, the inventory of the documents of the Patriarchate of Aquileia composed in the last quarter of the 14th century).
- Date — gives the dating of the document. Dating will always be provided in the following format: day (if known), month (if known), and year (according to the Common Era dating). Sometimes a relative date will be given if a more detailed dating is not possible (e.g. "between 575 and 582").
- Place — features the toponym of the place where the document was issued. This toponym will always follow the conventions of the country to which the place belongs to in the present day. For example, Civitas Austrie will be rendered as Cividale, not Čedad; Iustinopolis will be rendered as Koper, not Capodistria or Kopar; Mugla will be rendered as Muggia, not Milje, etc. Even the places that have an official English toponym (e.g. Venice for Venezia and Vienna for Wien) will not be excepted from this rule in this particular field.
- Regesta — offers a brief summary of the document's contents.
- Subjects — indexes key historical actors featured in the document in order to make them easily searchable throughout the database. For example, a donation charter issued by the Emperor Henry IV to patriarch Ulrich of Aquileia will feature both persons under this field; by clicking on the name of any subject listed under this field, the user will be taken to a list of all the documents that feature this particular historical subject. Without exceptions, the names featured in this field will always be written in Latin (e.g. Henricus IV, rex Romanorum, imperator Imperii Romanorum for King Henry IV; Wodalricus I, de domo comitum de Wimmare et Orlagemunde, marchio Carniole, marchio Istrie, for Margrave Ulrich I of Weimar-Orlamünde; Iustinopolis, commune, for the Commune of Koper, etc.)
- Source — features the physical location of the codex optimus, primary source upon which the transcription is made. Thus, the type of edition favored in the database is the so-called "best-manuscript edition" and not the "Lachmannian critical edition". If the document is fully preserved in the well-preserved, fully readable original, the field will not feature the locations of later copies; if the source is preserved only in later copies, the field will usually list only the most representative copies that are closest to the lost original. Originals are always marked and referred to as A, the copies as B, C, D, etc. Sometimes, especially with very old editions, locating the original is very difficult as editors would simply put "from the Archive in Vienna" or "from the Venetian archives" instead of providing more details. One of the goals of the project is to offer as detailed information as possible in this field, but it will take time before all the entries feature detailed information in this field. Also, some original sources have been lost since the times of 18th- or 19th-century editors.
- Previous Editions — features the publication of the best edition of the document from which the transcription of the source is used and adjusted according to these editorial principles. The field will not necessarily feature all the existing editions of the document, but only the editor's selection.
- FIM Edition — states what type of edition is published in the database. These can be:
- Diplomatic: an edition based on the original or best manuscript (the most common type of edition in FIM);
- Reconstructive: a Lachmannian type critical edition whereby a lost original is reconstructed based on later manuscript traditions;
- Adapted Replica: a copy of the edition referenced in the Previous Editions field edited according to conventions here outlined (only in those cases where the editor has not yet been able to find and/or consult the manuscript).
- Transcription — features the transcription of the source's contents and follows these conventions:
- Editor's interpolations are put inside square brackets 
- Parts of the text judged to be later interpolations are put inside chevrons ⟨⟩
- Text originally written on the margins of a manuscript is put inside angle brackets <>
- Illegible part(s) of the text are rendered with three dots and put inside the square brackets [...]
- If a part of the text is omitted from the edition, this is signaled by om. (omissa, omittitur) inside of square brackets [om.]
- Empty spaces left between words in the manuscript are referenced by three consecutive underscores ___
- Absolute fidelity to the lexical, grammatical, and syntactical forms of the original; absolutely no “corrections” of the authors’ Latin whatsoever.
- If dots appear in the manuscript, they are rendered as such in the transcription, but only up to five dots; anything upwards of five dots is always rendered as five dots.
- The letter “u” or “v” is rendered as a “v” when standing for a consonant sound and as a “u” when standing for a vowel.
- All the cases of “j” are rendered as an “i”.
- All the cases of a “y” at the end of a word standing for “ii” are rendered as “ii”.
- The numbers, where the editor can consult the original document, are not expanded and written out; IVor in the original standing for the cardinal number four (4) is rendered as “IVor”, just like XIIcima standing for the ordinal number twelfth (12th) is rendered as “XIIcima”. Arab numerals are also not expanded and written out.
- Absolutely all the other contractions and abbreviations are expanded.
- Standard graphical signs are rendered as follows:
- “(S)” for a handwritten sign of the witnesses;
- “(SN)” for a sign of the scribe or notary,
- “(SC)” for a Chrismon or a sign of the cross;
- “(SM)” for a monogram of a sovereign king or emperor;
- “(SR)” for a signum recognitionis;
- “(SI)” for an impressed seal (sigillium impressum);
- “(SP)” for a hanging seal (sigillium pendens);
- “(SI D)” for a seal that subsequently fell off (sigillium deperditum);
- “(R)” for a papal rota;
- “(+)” for the symbol designating the accepted proposals voted for in the Venetian councils.
- Capitalization is regularized and follows present day conventions; titles of offices and ranks are not capitalized (e.g. imperator, rex, marchio, patriarcha, episcopus, etc.), but the titles of institutions and geo-administrative regions are capitalized (e.g. Imperium, Regnum, Marchionatus, Patriarchatus, Episcopatus, etc.); adjectives derived from proper nouns are capitalized (e.g. patriarcha Aquileiensis, denarii Veronenses, etc.); names of days and months are not capitalized (e.g. die veneris, undecima mensis madii); the noun Deus and all the nouns and pronouns standing for Deus and Iesus are capitalized (quod Deus avertat, anno Eius nativitatis, anno Dominice incarnationis, in nomine Patris, Filii et Spiritus Sancti, etc.); adjectives qualifying sainted or beatified persons are not capitalized (sancti Fortunatus et Hermagoras, sanctus Maurus, beatus Bertrandus, beata virgo Maria, etc.); when standing for the community and not a specific building the noun Ecclesia is always capitalized.
- Modern punctuation is introduced; reported speech is always preceded by a colon and put between quotation marks (Et dixit Vantus Iohanne: “Va con Dio.”).
- In cases where a document is a mere derivative of an earlier source, the identical parts in the derived document are rendered in petite fonts, the missing parts are marked by a star (*) and the original parts are written in standard font.
- Critical apparatus — gives various notes on the text of the manuscript and, in cases of a critical edition based on a number of different manuscripts, lists readings from other copies. The abbreviations used in the apparatus criticus are the following:
add. – addidit / aditio
al. man. – alia manus
canc. – cancellavit
cf. – confer
coni. – coniecit / conicimus / coniectura
def. – deficit
des. – desinit
dub. – dubitanter / lectio dubia
ed. – edidit / editio
em. – emendavit / emendatio
eras. – erasit
ex corr. – ex correctione
exp. – expunxit
expl. – explicit
in marg. (d. / inf. / sin. / sup.) – in margine (dextra / inferiore / sinistra / superiore)
incip. – incipit
inf. (l) – infra (lineam)
inv. – invertit
iter. – iteravit
lac. – lacuna
lit. – litura / liturae
leg. – legit / legimus
lect. – lectio
man. r. – manus recentior
obsc. – obscurum (difficile legitur)
om. – omisit
(in) ras. – (in) rasura
sec. – secundum
seq(q). – sequens (sequentes)
fort. – fortasse
sig. abbr. – signum abbreviationis
sup. (l.) – supra (lineam)
Vulg. – Vulgata Sacrae Scripturae interpretatio
- Translation — provides either a published or (yet) unpublished translation of the document’s contents into English, Italian, and/or Croatian; the translation is planned only for documents of particular importance for the historical trajectory of Istria in order to make them accessible to a broader audience, such as pupils and students; the sources of published translations are always cited.
- Mapped toponyms — displays the toponyms mentioned in the document on a contemporary map via Google Maps interface.
- Medieval recollections — provides the texts of medieval regesta of the edited document or the narrative descriptions of the events featured in the document by medieval chroniclers.
- Selected bibliography — lists key publications dealing with the edited source.
- Editor’s notes — provide additional information regarding various aspects of the edited source.
- How to cite — suggests one possible way of referencing the database entry in the critical apparatus.
- Facsimile — displays the digital reproduction of the primary source upon which the edition is based.
- Image source and info — gives detailed information on the source of the image and its copyright, as well as on all the additional markup done by the editor (usually a red line signaling the exact part of the manuscript folio that is transcribed).