What is the meaning of D1, D2, D3, C1, C2, C3 etc in Kraken Report

[Rohit-Satyam]

Hi

Pardon me if I missed something in the Kraken2 manual.
I was going through the Kraken2 reports generated using Struo2 Kraken2 indexes and NCBI Refseq indexes. And though I understand what U, R, D, P, C, O, F, G, S, S1 means in a Kraken2 report generated by Struo2 Kraken2 Indexes, I don't understand what does numbers represents in the following U, R, D, P, C, O, F, G, S, S1C, C1, C2, C3, C4, D, D1, D2, D3, D4, F, F1, F2, F3, G, G1, G2, G3, K, K1, K2, K3, O, O1, O2, O3, O4, P, P1, P2, P3, P4, P5, P6, R, R1, R2, S, S1, S2, S3, U (This is from kraken2 results obtained when using RefSeq indexes)? Any why they are 4 (C1-C4 and D1-D4) in some and goes to 6 in some (P1-P6)?

[nick-youngblut]

What input files are you using for running Kraken2?