Grammar railroad diagram

Using a custom parser that translates `dbml/parser.pegjs` grammar to an EBNF understood by https://www.bottlecaps.de/rr/ui and manually fixing small errors we can have nice railroad diagram (https://en.wikipedia.org/wiki/Syntax_diagram) to help show/understand the syntax.

Copy and paste the EBNF shown bellow at https://www.bottlecaps.de/rr/ui on the tab Edit Grammar then click on the tab View Diagram.

```
//To be viewd at https://www.bottlecaps.de/rr/ui

rules ::=
expr*

expr ::=
TableSyntax
| RefSyntax
| EnumSyntax
| TableGroupSyntax
| ProjectSyntax
| __

TableSyntax ::=
table sp+ schema_name? name alias_def? sp* TableSettings? _ "{" TableBody "}"

RefSyntax ::=
ref_long
| ref_short

EnumSyntax ::=
enum sp+ schema_name? name _ "{" EnumBody "}"

TableGroupSyntax ::=
table_group sp+ schema_name? name _ "{" _ table_group_body _ "}"

ProjectSyntax ::=
project ( __ name )? _ "{" _ ProjectBody _ "}"

__ ::=
( comment | whitespace )+

project ::=
"project"

name ::=
character+
| ( quote [^\"\n]+ quote )

_ ::=
( comment | whitespace )*

ProjectBody ::=
_ ProjectElement* _

ProjectElement ::=
( _ ObjectNoteElement _ )
| ( _ TableSyntax _ )
| ( _ RefSyntax _ )
| ( _ EnumSyntax _ )
| ( TableGroupSyntax _ )
| ( _ ProjectField _ )

ObjectNoteElement ::=
ObjectNote
| ( "note" _ "{" _ StringLiteral _ "}" )

ProjectField ::=
name _ ":" _ StringLiteral

StringLiteral ::=
( '"' DoubleStringCharacter* '"' )
| ( "'''" MultiLineStringCharacter* "'''" )
| ( "'" SingleStringCharacter* "'" )

table_group ::=
"TableGroup"

sp ::=
" "

schema_name ::=
name "."

table_group_body ::=
( schema_name? name __ )*

ref_long ::=
ref ( __ name )? _ "{" _ ref_body _ "}"

ref_short ::=
ref ( sp+ name )? sp* ":" sp* ref_body

ref ::=
"ref"

ref_body ::=
field_identifier sp+ relation sp+ field_identifier sp* RefSettings?

field_identifier ::=
( name "." name "." RefField )
| ( name "." RefField )

relation ::=
[>-<]

RefSettings ::=
"[" RefSetting ( Comma RefSetting )* "]"

RefField ::=
RefSingleField
| RefMultipleFields

RefSingleField ::=
name

RefMultipleFields ::=
"(" sp* RefSingleField ( sp* Comma sp* RefSingleField )* sp* ")"

Comma ::=
","

RefSetting ::=
( _ OnUpdate _ )
| ( _ OnDelete _ )

OnUpdate ::=
"update:" _ ( no_action | restrict | cascade | set_null | set_default )

OnDelete ::=
"delete:" _ ( no_action | restrict | cascade | set_null | set_default )

no_action ::=
"no action"

restrict ::=
"restrict"

cascade ::=
"cascade"

set_null ::=
"set null"

set_default ::=
"set default"

table ::=
"table"

alias_def ::=
sp+ "as" sp+ name

TableSettings ::=
"[" TableSetting ( Comma TableSetting )* "]"

TableBody ::=
_ Field+ _ TableElement* _

Field ::=
_ name sp+ schema_name? type ( sp+ constrain )* ( sp+ FieldSettings )? sp* comment? newline

TableElement ::=
( _ Indexes _ )
| ( _ ObjectNoteElement _ )

Indexes ::=
_ indexes _ "{" IndexesBody "}"

type ::=
type_name ( sp* "(" sp* expression sp* ")" )?

constrain ::=
unique
| pk

FieldSettings ::=
"[" FieldSetting ( Comma FieldSetting )* "]"

comment ::=
single_line_comment
| multi_lime_comment

newline ::=
"\r\n"
| "\n"

enum ::=
"enum"

EnumBody ::=
_ EnumValue+ _

EnumValue ::=
_ name sp* EnumSetting? sp* comment? newline

EnumSetting ::=
"[" _ ObjectNote _ "]"

ObjectNote ::=
"note:" _ StringLiteral

FieldSetting ::=
( _ "not null" _ )
| ( _ "null" _ )
| ( _ "primary key" _ )
| ( _ "pk" _ )
| ( _ "unique" _ )
| ( _ "increment" _ )
| ( _ ObjectNote _ )
| ( _ RefInline _ )
| ( _ Default _ )

TableSetting ::=
( _ ObjectNote _ )
| ( _ HeaderColor _ )

HeaderColor ::=
_ header_color ":" _ sharp hex_color _

RefInline ::=
"ref:" sp* relation sp+ inline_field_identifier

Default ::=
"default:" _ DefaultVal

indexes ::=
"indexes"

IndexesBody ::=
_ Index+ _

Index ::=
_ ( SingleIndexSyntax | CompositeIndexSyntax ) _

SingleIndexSyntax ::=
_ SingleIndex sp* IndexSettings?

CompositeIndexSyntax ::=
_ CompositeIndex sp* IndexSettings?

SingleIndex ::=
( name sp* )
| Expression

IndexSettings ::=
( "[" sp* pk sp* "]" )
| ( "[" IndexSetting ( Comma IndexSetting )* "]" )

CompositeIndex ::=
"(" sp* SingleIndex ( Comma sp* SingleIndex )* ")"

Expression ::=
"`" [^`]* "`"

pk ::=
"pk"

IndexSetting ::=
( _ "unique" _ )
| ( _ IndexName _ )
| ( _ IndexType _ )
| ( _ ObjectNote _ )

IndexName ::=
"name:" _ StringLiteral

IndexType ::=
"type:" _ ( btree | hash )

btree ::=
"btree"

hash ::=
"hash"

inline_field_identifier ::=
( name "." name "." name )
| ( name "." name )

DefaultVal ::=
StringLiteral
| Expression
| BooleanLiteral
| NumberLiteral

BooleanLiteral ::=
'true'
| 'false'
| 'null'

NumberLiteral ::=
"-"? ( float | integer )

header_color ::=
"headercolor"

sharp ::=
"#"

hex_color ::=
six_char
| three_char

six_char ::=
hex_char hex_char hex_char hex_char hex_char hex_char

three_char ::=
hex_char hex_char hex_char

hex_char ::=
[0-9a-fA-F]

unique ::=
"unique"

as ::=
"as"

character ::=
[a-zA-Z0-9_]

quote ::=
'"'

type_name ::=
type_character+
| ( quote [^\"\n]+ quote )

type_character ::=
character
| [#x5B#x5D]

expression ::=
factor*

factor ::=
( character+ sp* "(" expression ")" )
| ( "(" expression ")" )
| ( exprCharNoCommaSpace+ ( sp* | "," | ");" | ( endline ");" ) ) )
| ( exprChar+ . )

exprCharNoCommaSpace ::=
[\'.a-zA-Z0-9_+-]

endline ::=
sp* newline

exprChar ::=
[\',.a-zA-Z0-9_+-`]
| sp
| newline
| tab

tab ::=
"\t"

allowed_chars ::=
_NOT_ ( '{' | '}' | whitespace_quote ) .

whitespace_quote ::=
[ \t\r\n\r\"]

whitespace ::=
[ \t\r\n\r]

single_line_comment ::=
"//" [^\n]*

multi_lime_comment ::=
"/*" ( _NOT_ "*/" . )* "*/"

DoubleStringCharacter ::=
( '\\' '"' )
| ( _NOT_ '"' SourceCharacter )

MultiLineStringCharacter ::=
"\\'"
| ( "\\" "\\"+ )
| ( "\\" "\n"? )
| ( _NOT_ "'''" SourceCharacter )

SingleStringCharacter ::=
"\\'"
| ( _NOT_ "'" SourceCharacter )

SourceCharacter ::=
.

digit ::=
[0-9]

decimal_point ::=
dot

dot ::=
'.'

equal ::=
'='

float ::=
[0-9]+ "." [0-9]+

integer ::=
[0-9]+

//Added tokens for railroad generation
_NOT_ ::= '!'
_AND_ ::= '&'
```