It helps other templates check if a string is "shorter or equally long" vs. "longer" than a given length.
Usage
This template takes 3 to 4 unnamed parameters.
Here is how to check if the string "abcde" is 4 characters or less:
{{str ≤ len | abcde | 4
| Equal or shorter.
| Longer.
}}
Which returns this:
Longer.
Templates have a problem to handle parameter data that contains equal signs "=". But that is easily solved by using numbered parameters. Here we check if the string "ab=cde" is 100 characters or less:
{{str ≤ len
| 1 = ab=cde
| 2 = 100
| 3 = Equal "=" or shorter.
| 4 = Longer, not "=".
}}
Which returns this:
Equal "=" or shorter.
It probably is a good habit to always use the numbered parameters, since you might not know beforehand exactly how the data will look that your template will feed to this meta-template.
Parameters
Detailed parameter explanation:
{{str ≤ len
| 1 = A string
| 2 = A length
| 3 = Data to return/render when "shorter than or equally long".
| 4 = Data to return/render when "longer than".
}}
Empty or undefined strings are considered to be of 0 length.
Length values below 0 are considered to be 0.
Technical details
The potential alternative templates names {{str <= len}} or (for the opposite) {{str > len}} do not work in MediaWiki.
Even though this is a string handling template it uses efficient code. (While some of the other string handling templates are probably so heavy on the servers that we perhaps should not use them.)
Templates have problems to handle parameter data that contains pipes "|", unless the pipe is inside another template {{name|param1}} or inside a piped link [[Help:Template|help]]. Thus templates can not handle wikitables as input unless you escape them by using the {{!}} template. This makes it hard to use wikitables as parameters to templates. Instead the usual solution is to use "HTML wikimarkup" for the table code, which is more robust.
