I think it's a bug on the function or the documentation. I remember that I reported the inconsistency to Safe support four years ago, am surprised the issue is still outstanding.
Forgot the case number, but I found out this workspace which I sent to Safe in order to describe the issue at that time.
FindRegEx_b15539.fmw: created with FME 2015 build 15539, run with FME 2019.1.2

Hope someone from Safe clarifies this. @danatsafe
I think it's a bug on the function or the documentation. I remember that I reported the inconsistency to Safe support four years ago, am surprised the issue is still outstanding.
Forgot the case number, but I found out this workspace which I sent to Safe in order to describe the issue at that time.
FindRegEx_b15539.fmw: created with FME 2015 build 15539, run with FME 2019.1.2

Hope someone from Safe clarifies this. @danatsafe
@takashi Unfortunately the current doc is misleading. FindRegEx can't search backwards but the start of the forward search can be set from the end (counting backwards). @jingking If you expect FindRegEx to return 0 for 12345L, then instead try
@Evaluate(@StringLength(12345L)-1-@FindRegEx(12345L,L))
@takashi Unfortunately the current doc is misleading. FindRegEx can't search backwards but the start of the forward search can be set from the end (counting backwards). @jingking If you expect FindRegEx to return 0 for 12345L, then instead try
@Evaluate(@StringLength(12345L)-1-@FindRegEx(12345L,L))
Thanks for the clarification. That makes sense.