Regex pattern for FileService

Good day!
I am trying to use standard regex expression as a pattern field for querying files from fileservice API and it does not work.
All.pdf - this one works.
/^All..pdf/i - this one not, I tried to test at regex tester sites, and everything is okay, but backendless do not want to work with this pattern.
Any ideas?
Thanks for your help,
best,
Nick.

File service support only next rules

pattern- A pattern which the returned files and directories must match. The pattern can include wildcard characters. Asterisk (*) matches a substring of any length. Question mark (?) matches only one character in the file/directory name.
doc: https://backendless.com/documentation/files/android/file_directory_listing.htm

so you can use only asterisk(*) or question mark in your queries

Thanks for your help.