Annotations in sequence labels
Many usearch command support or require annotations in sequence labels.
Annotations indicate attributes of a sequence such as its abundance, sample
identifier, taxonomy etc. There are no generally accepted standards for
including annotations in FASTQ or FASTA files, so annotations are not
usually compatible with other software packages.
Most annotations have the form name=value.
In usearch, annotations are separated by semi-colons. The first annotation
begins at the first semi-colon. The label up to the first semi-colon is
sometimes understood to be an implied name, e.g. an OTU identifier.
A semi-colon terminating the last annotation at the end of the label is
optional, but recommended.
White space (blanks and tabs) are allowed within annotations, but are
discouraged because they can cause problems. For example, if a sequence
label has a tab and is written to a tab-separated text file, then the number
of fields will be messed up.