Clarify that formal holidays are what is commonly called statutory holidays

README.md

@@ -7,6 +7,8 @@ Currently it is only used by the [existing Holidays gem](https://github.com/holi
 definitions and generates ruby classes for use in that gem. In the future it will be used by other languages in
 a similar manner.
 
+By default the definitions in this repository represent **statutory holidays** (formally government-defined observances). Holidays that are culturally recognized but not enshrined in law (such as Valentine's Day) are marked `type: informal` and are only returned when the consumer explicitly requests them. See the [Syntax Guide](doc/SYNTAX.md#formalinformal) for details.
+
 **Please note** that this is _not_ a gem. The validation process is written in ruby simply for convenience. The real
 stars of this show are the YAML files.
 

doc/SYNTAX.md

@@ -37,7 +37,7 @@ Non-standard regions (e.g. `ecbtarget`, `federalreserve`, etc) must be all one w
 
 #### `formal`/`informal`
 
-We consider `formal` dates as government-defined holidays. These could be the kinds of holidays where everyone stays home from work or perhaps are bank holidays but it is *not required* for a holiday to have these features to be considered formal.
+We consider `formal` dates as government-defined holidays, what are commonly called **statutory** holidays. These could be the kinds of holidays where everyone stays home from work or perhaps are bank holidays but it is *not required* for a holiday to have these features to be considered formal.
 
 `Informal` holidays are holidays that everyone knows about but aren't enshrined in law. For example, Valentine's Day in the US is considered an informal holiday.