Minecraft wiki entry for data, associated text: ... modify (block <targetPos>|entity <target>|storage <target>) <targetPath> ...
... append from (block <sourcePos> entity <source> storage <source>) [<sourcePath>]
... append value <value>
Append the source data onto the end of the pointed-to list.
... insert <index> from (block <sourcePos> entity <source> storage <source>) [<sourcePath>]
... insert <index> value <value>
Insert the source data into the pointed-to list as element <index>, then shift higher elements one position upwards.
... merge from (block <sourcePos> entity <source> storage <source>) [<sourcePath>]
... merge value <value>
Merge the source data into the pointed-to object.
... prepend from (block <sourcePos> entity <source> storage <source>) [<sourcePath>]
... prepend value <value>
Prepend the source data onto the beginning of the pointed-to list.
... set from (block <sourcePos> entity <source> storage <source>) [<sourcePath>]
... set value <value>
Set the tag specified by <targetPath> to the source data.