start: complex (ATTR_SEP global_attr)*
complex: component (PLUS_SEP component)*
component: coefficient? subunit
coefficient: INT STAR_SEP
subunit: NAME
global_attr: crosslink
crosslink: "x-link" FIELD_SEP "[" WS* (onto_crosslink | inline_crosslink) WS* "]"

onto_crosslink: onto_crosslink_attr (ATTR_SEP onto_crosslink_attr)*
onto_crosslink_attr: onto_crosslink_type | onto_crosslink_monomer
onto_crosslink_type: "type" FIELD_SEP NAME
onto_crosslink_monomer: onto_crosslink_monomer_type FIELD_SEP subunit subunit_idx? "-" monomer_position
onto_crosslink_monomer_type: /(l|r)/

inline_crosslink: inline_crosslink_attr (ATTR_SEP inline_crosslink_attr)*
inline_crosslink_attr: inline_crosslink_atom | inline_crosslink_order | inline_crosslink_stereo | inline_crosslink_comments
inline_crosslink_atom: inline_crosslink_atom_type FIELD_SEP subunit subunit_idx? "-" monomer_position atom_element atom_position atom_component_type? atom_charge?
inline_crosslink_atom_type: /(l|r)/ "-" /(bond|displaced)/ "-atom"
inline_crosslink_order: "order" field_sep QUOTE_DELIMITER /(single|double|triple|aromatic)/ QUOTE_DELIMITER
inline_crosslink_stereo: "stereo" field_sep QUOTE_DELIMITER /(wedge|hash|up|down)/ QUOTE_DELIMITER
inline_crosslink_comments: "comments" FIELD_SEP ESCAPED_STRING

monomer_position: /[0-9]+/
subunit_idx: /\([0-9]+\)/
atom_element: /[A-Z][a-z]?/
atom_position: /[0-9]+/
atom_charge: /[\+\-][0-9]+/
atom_component_type: /[mb]/

?field_sep: WS? ":" WS?

NAME: /(?!(^|\b)(\d+(\.\d*)?(\b|$))|(\.\d+$)|(0[x][0-9a-f]+(\b|$))|([0-9]+e[0-9]+(\b|$)))[a-z0-9_]+/
PLUS_SEP: WS* "+" WS*
STAR_SEP: WS* "*" WS*
ATTR_SEP: WS* "|" WS*
FIELD_SEP: WS* ":" WS*
QUOTE_DELIMITER: "\""

WS: /[ \t\f\r\n]+/
INT: /[0-9]+/
ESCAPED_STRING: /"(?:[^"\\]|\\.)*"/