- attr
A named list or named vector, names are attribute names and values are attribute values.
- separate
TRUE/FALSE, If TRUE, returns separate tags for each item of attr if length of that item is greater than 1; if FALSE, returns one tag.
- collapse
A string. If NULL, returns a vector the same length as the longest item of attr, instead of one string.
- formatted
TRUE/FALSE, if TRUE, HTML will be generated with indents and new lines for readability at the cost of performance. Controlled by setting the environment variable html5_vars$formatted <- TRUE/FALSE