The Medline (txt) format can be used by a simple text document. Here, you have to write the field names at the beginning of each line. The Medline (xml) format is a XML document. The field name has to be written between < and >. For further information visit https://www.nlm.nih.gov/bsd/licensee/elements_descriptions.html. Medline (txt) and Medline (XML) always take the type "article". RIS works similar to Medline (txt) with the difference that different fields are supported and the file extension is "ris".
In other sources, you might encounter "MedlinePlain" as synonym for "Medline (txt)" and "Medline" as synonym for "Medline (xml)".
Abstract
AB
Abstract / AbstractText
AB
Affiliation
AD
Article Date
ArticleDate
Article Identifier
AID
Article
Article Title
ArticleTitle
Author
AU
AuthorList
AU/A1
Author Identifier
AUID
Book Title
BTI
BT
Chemical List
ChemicalList
Citation Subset
CitationSubset
Collection Title
CTI
Collaborators
A3
Comments Corrections List
CommentsCorrectionsList
Corporate Author
CN
Copyright Information
CopyrightInformation
Create Date
CRDT
Country
Country
Data Bank List
DataBankList
Date Completed
DCOM
DateCompleted
Date Created
DA
DateCreated
Date Last Revised
LR
DateRevised
Date of Electronic Publication
DEP
Date of Publication
DP
Y2
Delete Citation
DeleteCitation
DOI
DOI
Edition
EN
Editor and Full Editor Name
FED
ED
End
ER
End Page
EP
Entrez Date
EDAT
Full Author
FAU
Full Personal Name as Subject
FPS
Gene Symbol
GS
General Note
GN
GeneralNote
Grant List
GrantList
Grant Number
GR
Investigator Name and Full Investigator Name
IR/FIR
Investigator List
InvestigatorList
ISO Abbreviation
ISOAbbreviation
ISBN
ISBN
SN
ISSN
IS
ISSN
ISSN Linking
ISSNLinking
Issue
IP
Issue
IS
Journal Issue
JournalIssue
Journal Title
JT
Journal
JO/JF/JA
Journal Title Abbreviation
TA
Keywords
KeywordList
KW
Language
LA
Language
Location Identifier
LID
Manuscript Identifier
MID
Medline Title Abbreviation
MedlineTA
Medline Date
MedlineDate
MeSH Date
MHDA
Mesh Heading List
MeshHeadingList
MeSH Terms
MH
Misc
M1-M3
NLM Unique ID
JID
NlmUniqueID
Note
N1
Number of References
RF
Other Abstract and other abstract language
OAB/OABL
OtherAbstract
Other Copyright Information
OCI
Other ID
OID
OtherID
Other Term
OT
Other Term Owner
OTO
Owner
OWN
Pagination
PG
Pagination
Personal Name as Subject
PS
Personal Name as Subject List
PersonalNameSubjectList
Place of Publication
PL
Publication History Status
PHST
Publication Status
PST
Publication Type
PT
Publication Type List
PublicationTypeList
Publisher
PB
Publishing Date
PubDate
Publishing Model
PUBM
PubMed Central Identifier
PMCR
PubmMed Unique Identifier
PMID
PMID
Registry Number
RN
Reprint
RP
Start Page
SP
Substance Name
NM
Supplemental Mesh List
SupplMeshList
Secondary Source ID
SI
Source
SO
Space Flight Mission
SFM
Status
STAT
Subset
SB
Title
TI
Title
TI/T1
Transliterated Title
TT
Type
TY
URL
UR
User Text
U1-U3
Volume
VI
Volume
VL
Volume Title
VTI
Vernacular Title
VernacularTitle
Year
PY/Y1