This seems to work well enough to satisfy https://easyeda.com/editor.

Label:
Added descriptions of the values for JUSTIFICATION
Add ISMIRRORED

“Middle” seems to be the middle of lower-case letters, while “central” seems
to be the middle of upper-case letters.

Information taken from Wisamasd’s commit message. TK does not allow different
arrow kinds at each end; need to redo the arrow API.

Add optional properties  for Polyline:
LINESHAPESIZE, can take values:
none(-1 ?) - Smallest
1 - Small
2 - Medium
3 - Large

STARTLINESHAPE, can take values as ENDLINESHAPE:
none(-1 ?) - Smallest - None
1 - Arrow
2 - SolidArrow
3 - Tail
4 - SolidTail
5 - Circle
6 - Square

Update format.md with some additional info. Also note: RECORD=2 may be in a binary format in later versions of Altium Designer.