/^(?:bl|_)|\.\d{3}\.\d{3,}$/i
 ^     ^  ^ ^ ^    ^ ^    ^ ^       
 |     |  | | |    | |    | |       
 |     |  | | |    | |    | + - Case-insensitive
 |     |  | | |    | |    + - From the end of the string
 |     |  | | |    | + - Three or more digits
 |     |  | | |    + - A decimal point
 |     |  | | + - Three digits
 |     |  | + - A decimal point
 |     |  + - OR
 |     + - Match either "bl" or "_"
 + - From the beginning of the string