diff -r 3192dc8772de -r 7d309accc639 src/FreeformASN1ContentHandler.h
--- a/src/FreeformASN1ContentHandler.h	Tue Jul 27 18:33:27 2021 +0200
+++ b/src/FreeformASN1ContentHandler.h	Wed Jul 28 18:01:09 2021 +0200
@@ -26,6 +26,11 @@
 namespace in {
 namespace asn1 {
 
+namespace freeformOption {
+static const char* BitStringSymbol0 = "bit-string-symbol-0";
+static const char* BitStringSymbol1 = "bit-string-symbol-1";
+}
+
 /**
  * Converts arbitrary ASN.1 stream of events to a relation
  * i.e. does not require any specific structures/schema.
@@ -40,6 +45,9 @@
 	Configuration configuration;
 	std::vector<relpipe::common::type::Integer> position;
 
+	std::string bitStringSymbol0 = "0";
+	std::string bitStringSymbol1 = "1";
+
 	class Record {
 	public:
 		const Header* header;
@@ -105,7 +113,11 @@
 	}
 
 	bool setOption(const std::string& uri, const std::string& value) override {
-		return false;
+		if (uri == freeformOption::BitStringSymbol0) bitStringSymbol0 = value;
+		else if (uri == freeformOption::BitStringSymbol1) bitStringSymbol1 = value;
+		else return false;
+
+		return true;
 	}
 
 	void writeStreamStart() override {
@@ -131,7 +143,7 @@
 	void writeStreamEnd() override {
 		Record r(nullptr, position, L"stream-end");
 		write(r);
-		
+
 		auto id = position.back() + 1;
 		position.pop_back();
 		position.back() = id;
@@ -147,7 +159,7 @@
 	void writeCollectionEnd() override {
 		Record r(nullptr, position, L"collection-end");
 		write(r);
-		
+
 		auto id = position.back() + 1;
 		position.pop_back();
 		position.back() = id;
@@ -155,8 +167,7 @@
 
 	void writeBitString(const Header& header, std::vector<bool> value) override {
 		std::stringstream bits;
-		for (bool b : value) bits << (int) b;
-		// for (bool b : value) bits << (b ? ':' : '.'); // TODO: configurable true/false symbols?
+		for (bool b : value) bits << (b ? bitStringSymbol1 : bitStringSymbol0);
 
 		position.back()++;
 		Record r(&header, position, L"bit-string");