Template:Year by category/doc

Purpose
This template is intended to be used in year-based categories where the year is the first thing in the category name (for example, 2008 in Canadian music or 1979 disasters). It creates a "timeline" style table of links to categories for adjacent years before or after it in the same decade (see example below).

Parameters
The first 5 parameters split the name of the category page receiving the template into separate pieces. They are used to form the timeline links.
 * m = millennium digit
 * c = century digit
 * d = decade digit
 * y = year digit
 * The single-digit values of these 4 parameters, taken together ("mcdy"), form the four-digit year. If the year is before 1000 (and thus only 3 digits long) or even earlier, parameters can be omitted, as necessary.
 * cat = category name suffix
 * The portion of the category name after the year, including the word "in" if present.

The next parameter can be used to link to a "main article" for the category.
 * in = see also article name suffix
 * Optional: Adds a "see also" link to a closely related "year-in" article. This suffix should not contain the year or the word "in", which is provided by the template itself.

The rest of the parameters are used to categorize the page containing the template. Note that both the "parent" and "subcat" parameters are referring to parent categories of the category page the template is being placed on.
 * parent = parent category name
 * Optional: Full name (not including "Category:" prefix) of the category into which this category and similar categories for other years will all be placed (typically, but not always, named something like " topic by year"). Note that a sortkey is not used, so the sorting will be by year.
 * subcat = different category name
 * Optional: The full name (not including the "Category:" prefix) of another appropriate parent category, typically for the same year. If omitted, the current category will be placed in the category for the year itself, using the value of the "cat" parameter as the sortkey (note that this will not be acceptable if the value of "cat" begins with the word "in").
 * sortkey = category sortkey text
 * The sortkey used on the category link created by the previous parameter. If "subcat" is used but "sortkey" is not specified, a blank sortkey will be used.

Using all parameters
When placed on the page Category:2008 in Canadian music:
 * displays the following "timeline" and "see also" article link:


 * places the page into Category:Canadian music by year (sorted by year) and Category:2008 in Canada (using the sortkey "Music", which is appropriate since everything in the latter category already pertains to 2008 and Canada)

Using some parameters
When placed on the page Category:1999 disasters:
 * displays the following "timeline" (note that the last year isn't linked, since it would be a reference to the same category the template is on):


 * places the page into Category:20th-century disasters (sorted by year) and (since "subcat" wasn't specified) Category:1979 (using the sortkey "disasters")

Subtemplate

 * Year by category/core

Tracking categories
These are populated by the sub-template YearParamUsageCheck: