FSI constant Null safety
U+2068 FIRST STRONG ISOLATE
Treat the following text as isolated and in the direction of its first strong directional character that is not inside a nested isolate.
This essentially "auto-detects" the directionality of the text. It is not 100% reliable. For example, Arabic text that starts with an English quote will be detected as LTR, not RTL, which will lead to the text being in a weird order.
Use PDI to end the isolated scope.
Implementation
static const String FSI = '\u2068';