[2] They may be printed in various styles (e. g., linked, nested, indented, graphically branching) or used as interactive, computer-aided keys.
Any single-access key organizes a large set of items into a structure that breaks them down into smaller, more accessible subsets, with many keys leading to the smallest available classification unit (a species or infraspecific taxon typically in the form of binomial nomenclature).
Multiple diagnostic keys may be offered for the same group of organisms: Diagnostic keys may be designed for field (field guides) or laboratory use, for summer or winter use, and they may use geographic distribution or habitat preference of organisms as accessory characteristics.
To achieve this, these keys often have to use more difficult characteristics, which may not always be available in the field, and which may require instruments like a hand lens or microscope.
Synoptic keys are typically found in scientific treatments of a taxonomic group ("monographs").
However, the latter consideration can easily be accommodated in a polytomous key where couplets based on a single characteristic may have more than two choices, and complex statements may be limited to two alternative leads.
With a short key and moderate indentation it can be easy to follow and even backtrace an erroneous identification path.
A large amount of knowledge about reliable and efficient identification procedures may be incorporated in good single-access keys.
Although software exists that helps in skipping questions in a single-access key,[3] the more general solution to this problem is the construction and use of multi-access keys, allowing a free choice of identification steps and are easily adaptable to different taxa (e.g., very small or very large) as well as different circumstances of identification (e. g., in the field or laboratory).