This question illustrates a perennial problem with manuscript transcription: there is no single book of standards that is universally applied! To quote from David L. Vander Meulen and G. Thomas Tanselle:
There has never been a single standard convention for the transcription of manuscript texts, and it is not likely that there will ever be one, given the great variety of textual complications that manuscripts - from all times and places - can present.
In general, particular institutions have their own standards for transcription. We just have to get used to them. For anyone who is fairly new to the subject, I would usually recommend reading every transcription manual they can get their hands on. These will often contain include rules and guidance that are very different from the standards we were taught, and give some insight into the variety that we encounter out in the 'real world'!
- This text is from a hymn, Verbum Supernum Prodiens by Thomas Aquinas
The indentation that you noted:
Verbum supernum prodiens,
Nec Patris linquens dexteram,
Ad opus suum exiens,
Venit advitae vesperam.
indicates that, for the purpose of the sequence, the 2nd and 4th lines are continuations of the 1st & 3rd respectively. Thus, lines 1 & 2 form a 'couplet', lines 3 & 4 form a 'couplet', etc.
This format is still occasionally used in modern English translations, thus for the verse above it would be:
The Word of God proceeding forth,
Yet leaving not the Father's side,
And going to His work on earth,
Had reached at length life's eventide.
- The double angle brackets,
», simply indicate speech.
The single brackets on
<hor> indicate that the first part of the word was missing, and that 'hornas' is the postulated reconstruction.
In the case of the Finnsburg Fragment, this is especially problematic since the original manuscript has since been lost, and all we have today is a transcription made in 1705. For more on this, you might find Finnsburh: Fragments of Fact, Fiction, and History by Kayse Schmucker of interest.
For a fully diacritically-marked text and translation, see the Finnsburh Fragment on Beowulf on Steorarume.
- Square brackets serve a number of functions when transcribing manuscripts. Here, they seem to be used refer to letters or words that have been inserted into the transcription. This can be for a variety of reasons, for example because a well-known abbreviation in the original has been expanded, or because it appears the original scribe missed out a letter.
For the Owl and Nightingale, if we look at the original manuscript text the reasons for the use of square brackets in this case become clear:
Ich was in one sumere dale,
in one suthe diyhele hale,
iherde ich holde grete tale
an hule and one niyhtingale.
That plait was stif & starc & strong,
sum wile softe & lud among;
an aither ayhen other sval,
& let that [vue]le mod ut al.
& either seide of otheres custe
that alre-worste that hi wuste:
& hure & hure of othere[s] songe
The first expands the abbreviation in the eighth line, and the second supplies the letter 's' that seems to have been omitted by the original scribe.
- This is from the Wessobrunn Prayer
As noted in the Wikipedia article, it appears from the context that the word 'sterro' ('star') was omitted by the scribe. The angle brackets are used here to indicate that the transcriber has corrected the (presumed) error by the scribe.
- The indentation in the Kyrie eleison indicates what we might term the 'chorus', which in modern liturgy might be in the form of a 'call and response'
Priest: Kyrie eleison (Lord, have mercy)
All: Christe eleison (Christ, have mercy)
The vertical bars in the transcription are used, correctly, to indicate the beginnings of the lines in the original manuscript (which can be seen above the transcription for that example). However, they seem to stray from the standard here in that they are not using a double vertical line to indicate the fifth line.
- This looks to be a really good example of where the transcribers have completely discarded the Leiden Conventions on transcription. The transcription is from the Cantar de Mio Cid.
The vertical bars do not indicate the start of a new line in the original manuscript, as we can see when we examine the original manuscript:
Comparing with the given transcription:
De los sos ojos | tan fuerte mientre lorando
tornava la cabeça | y estava los catando.
Vio puertas abiertas | e uços sin cañados,
alcandaras vazias | sin pielles e sin mantos
e sin falcones e sin adtores mudados.
Sospiro mio Çid | ca mucho avie grandes cuidados.
Ffablo mio Çid | bien e tan mesurado:
«¡Grado a ti, señor, | padre que estas en alto!
¡Esto me an buelto | mios enemigos malos!»
It appears that your surmise here is correct, and the vertical bars are being used in this case to indicate half-lines in the poem.
Many publications will include a brief explanation of the conventions adopted in transcribing manuscripts or papyri. Most will conform - to a greater or lesser degree - with the Leiden System, established in the 1930s.
Unfortunately, many transcriptions available online don't include any key to the symbols and conventions being used. In those cases you just have to use your best judgement. However, it will get easier as you gain more experience.
As regards changing the symbols and conventions being used, I would suggest:
- If they already comply reasonably well with the Leiden System leave
them as they are.
- If they are significantly different from the Leiden System, consider
modifying them so that they do comply with the Leiden System. After
all, the goal is for others to read and understand your transcriptions, so
conforming to a 'standard' system is highly desirable.