I am using the gencode v19 gtf file for annotation of my chipseq data ( source - ftp://ftp.sanger.ac.uk/pub/gencode/Gencode_human/release_19/) and the description of the format of the file (http://www.gencodegenes.org/gencodeformat.html) mentions that there is an optional field called transcript_support_level. However I cannot find that information for any of the records in the gtf file nor does any other data file in the release has that information.
Surprisingly though, in the UCSC browser, for all gencode transcripts, the transcript support level has been mentioned ( which to me seems like that there should be a file somewhere that contains this tag). The gtf files from UCSC gencode track/Ensembl FTP also do not contain this record.
Has anybody used this field before ? and if so how ? Does anybody have an idea on where can I source the data sheet that would contain the transcript support level information ?