Is an object an exdf?
is.exdf.RdChecks whether an object is an exdf object.
Details
The default version of is.exdf simply checks to see if 'exdf'
  is in class(x).
If consistency_check is TRUE, then additional checks will be
  performed to make sure the object has three elements named main_data,
  units, and categories; that these elements are data frames with
  the same column names; and that units and categories each have
  one row. These requirements are all part of the definition of an exdf
  object, but these checks require additional time so they are not always
  desired.
Examples
# Test a simple exdf object
simple_exdf <- exdf(data.frame(A = 1), data.frame(A = 'u'), data.frame(A = 'c'))
is.exdf(simple_exdf)
#> [1] TRUE
is.exdf(simple_exdf, TRUE)
#> [1] TRUE
# Test an object that is clearly not an exdf
not_an_exdf <- 2
is.exdf(not_an_exdf)
#> [1] FALSE
is.exdf(not_an_exdf, TRUE)
#> [1] FALSE
# Test an object that claims to be an exdf but does not meet all of the
# requirements
fake_exdf <- not_an_exdf
class(fake_exdf) <- c('exdf', class(fake_exdf))
is.exdf(fake_exdf)
#> [1] TRUE
is.exdf(fake_exdf, TRUE)
#> Warning: x must have elements named `main_data`, `units`, and `categories`
#> [1] FALSE