Under-exploited table elements Tables

Discover a series of barely unknown table elements. As presented at the Web Experience Toolkit Codefest 4.

Who they are?

colgroup [span]: Don't know that elements exists. Even if in the table a scope="colgroup" is used for a th.
col [span]: Use to apply styling per table column.
thead: Rarely use, except of a tbody is coded explicitly so it used to group the column header cells together.
tbody: Seems useless, added automaticly by the browser. Have no clue that elements could have multiple instances. Unaware that only one scope="rowgroup" could exist per tbody
tfoot: Use to link carry table notes/reference.

colgroup [span]: Represents a group of one or more columns in the table.
col [span]: Represents one or more columns in the column group represented by that colgroup.
thead: Represents the block of rows that consist of the column labels (headers) for the parent table element.
tbody: Represents a block of rows that consist of a body of data for the parent table element.
tfoot: Represents the block of rows that consist of the column summaries (footers) for the parent table element.

Column styling: Understand the meaning provided by that styling. Research how other, worldwide and media wide, represents that kind of information. Try multiple prototype that implement alternate design. The goal is to ensure the styling is applied to highlight the purpose (like a total) and not the contextual use of the data.
Table notes / reference: Use footnote or to be included in prose, surrounding the table.