Convert indent to tabs (fix IDE setting).
WIP: Changes to support empty separators in multipart ID generators.

+ Create `explodeValue` method, which handles all separation of strings into the
  multipart value in a consistent manner.
+ Change all uses of base `explode` and related branching pattern into calls to
  `explodeValue` method.
+ Add missing local array variable declaration in `getNextValue` method.
+ Remove redundant explicit `implements` which is implicit through given `extends`.
+ Remove unused variables.
+ Fix error with undefined constant in `htmlFormValuesAsArray`.
+ Fix invalid HTML output (`SELECTED="SELECTED"` is valid).
+ Replace `$a ? $a : $b` form with `$a ?: $b` shorthand.
+ General code cleanup.
WIP: Changes to support empty separators in multipart ID generators.

+ Refactor `explodeValue` for readability.
+ Enhance `explodeValue` to handle LIST elements correctly.
Support empty separators in multipart ID generators.

+ Enhance `explodeValue` to handle all element types.
+ Change `width` configuration setting to secondary after determined width
  based on type.