Start definining variable identifiers

Variables are standard identifiers or literals that can be
augmented by accessors (either dictionary or dot style). This
finally defines what a string is.

tatsu_grammar.txt

@@ -68,7 +68,7 @@ block_parameter_value
 
 variable_expression
     =
-    variable_open IDENTIFIER { !variable_close variable_filter }* variable_close
+    variable_open variable_identifier { !variable_close variable_filter }* variable_close
     ;
 variable_open
     =
@@ -79,6 +79,17 @@ variable_close
     {SP}* @:"}}"
     ;
 
+variable_identifier
+    =
+    ( IDENTIFIER | STRING )
+    { variable_accessor }*
+    ;
+
+variable_accessor
+    =
+    "[" variable_identifier "]"
+    ;
+
 variable_filter
     =
     {SP}* "|" {SP}* @:filter
@@ -112,9 +123,24 @@ comment_content         = {!comment_close CHAR}* ;
 
 content                 = !(block_open | variable_open | comment_open) CHAR ;
 
+STRING
+    =
+    SINGLE_QUOTE_STRING | DOUBLE_QUOTE_STRING
+    ;
+
+SINGLE_QUOTE_STRING
+    =
+    "'" { !"'" ?'.' }* "'"
+    ;
+
+DOUBLE_QUOTE_STRING
+    =
+    '"' { !'"' ?'.' }* '"'
+    ;
+
 IDENTIFIER
     =
-    /[a-zA-Z][a-zA-Z0-9]*/
+    /[a-zA-Z_][a-zA-Z0-9_]*/
     ;
 
 ALPHA

test_template.jinja

@@ -1,5 +1,5 @@
 {% with key=val %}
-{{ kkk  |test(first ,second, third)|filter | lastFilter}}
+{{ dict_var['single']["double"]  |test(first ,second, third)|filter | lastFilter}}
 {%block single key=val param=value %}
 test {{var}}
 {%endblock%}