
begleitend
supplementary
Something that happens at the same time as a main thing or supplements it.
Begleitend zur Ausstellung gibt es einen ausführlichen Katalog.
As a supplement to the exhibition, there is a detailed catalog.
accompanying / supplementary
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supplementary
Something that happens at the same time as a main thing or supplements it.
Begleitend zur Ausstellung gibt es einen ausführlichen Katalog.
As a supplement to the exhibition, there is a detailed catalog.

accompanying
Escorting someone or something physically along a route or to a place.
Der Angeklagte wurde von zwei begleitenden Polizisten in den Gerichtssaal geführt.
The defendant was led into the courtroom by two accompanying police officers.
'Begleitend' (accompanying/supplementary) is the present participle of the verb 'begleiten' (to accompany). This form is used like an adjective and describes an action that takes place at the same time as something else.
Die begleitende Musik schuf eine entspannte Atmosphäre.
The accompanying music created a relaxed atmosphere.
In this meaning, 'begleitend' (supplementary) usually refers to abstract things that supplement a main thing, such as measures, music, or information. If it is about people escorting someone, the other, literal meaning is intended.
Begleitend zum Sprachkurs erhalten die Teilnehmer Lernmaterialien.
As a supplement to the language course, participants receive learning materials.
'Begleitend' (supplementary) is often used at the beginning of a sentence in the construction 'Begleitend zu + dative' (as a supplement to + dative). The verb then follows in position two.
Begleitend zur Konferenz findet eine Fachmesse statt.
As a supplement to the conference, a trade fair is taking place.
Common nouns combined with 'begleitend' (supplementary/accompanying) are 'Maßnahmen' (measures), 'Materialien' (materials), 'Symptome' (symptoms), or 'Umstände' (circumstances).
Fieber ist ein begleitendes Symptom der Grippe.
Fever is an accompanying symptom of the flu.
additional
Zusätzlich only indicates that another offer or service is available. Begleitend shows that this offer belongs alongside a main thing and supports or complements it at the same time. Use „zusätzlich“ for an independent extra; „begleitend“ may be more appropriate for a component assigned to a main offering.

Das Museum bietet begleitend zur Ausstellung einen Workshop an.
The museum offers a workshop to accompany the exhibition.
Das Museum bietet zusätzlich einen Workshop am Samstag an.
The museum also offers a workshop on Saturday.