--- ./src/libmime/mime_string.hxx	2026-06-12 07:07:05
+++ ./src/libmime/mime_string.hxx	2026-06-12 07:17:42
@@ -94,7 +94,7 @@
 		return idx != it.idx;
 	}
 
-	iterator_base(difference_type index, Container *instance) noexcept
+	iterator_base(difference_type index, const Container *instance) noexcept
 		: idx(index), cont_instance(instance)
 	{
 	}
@@ -103,7 +103,7 @@
 
 	iterator_base &operator=(const iterator_base &) noexcept = default;
 
-	Container *get_instance() const noexcept
+	const Container *get_instance() const noexcept
 	{
 		return cont_instance;
 	}
@@ -118,7 +118,7 @@
 
 protected:
 	difference_type idx;
-	Container *cont_instance = nullptr;
+	const Container *cont_instance = nullptr;
 
 protected:
 	void advance(difference_type n) noexcept
@@ -164,7 +164,7 @@
 		return idx != it.idx;
 	}
 
-	iterator_base(difference_type index, Container *instance) noexcept
+	iterator_base(difference_type index, const Container *instance) noexcept
 		: idx(index), cont_instance(instance)
 	{
 	}
@@ -172,7 +172,7 @@
 	iterator_base() noexcept = default;
 	iterator_base(const iterator_base &) noexcept = default;
 	iterator_base &operator=(const iterator_base &) noexcept = default;
-	Container *get_instance() const noexcept
+	const Container *get_instance() const noexcept
 	{
 		return cont_instance;
 	}
@@ -184,7 +184,7 @@
 
 protected:
 	difference_type idx;
-	Container *cont_instance = nullptr;
+	const Container *cont_instance = nullptr;
 
 protected:
 	//! Advance the iterator n times (negative values allowed!)
@@ -210,7 +210,7 @@
 
 template<typename Container, bool Raw = false>
 struct iterator : iterator_base<Container, Raw> {
-	iterator(typename iterator_base<Container, Raw>::difference_type index, Container *instance) noexcept
+	iterator(typename iterator_base<Container, Raw>::difference_type index, const Container *instance) noexcept
 		: iterator_base<Container, Raw>(index, instance)
 	{
 	}
@@ -523,17 +523,17 @@
 	}
 
 	/* Iterators */
-	inline auto begin() noexcept -> iterator
+	inline auto begin() const noexcept -> iterator
 	{
 		return {0, this};
 	}
 
-	inline auto raw_begin() noexcept -> raw_iterator
+	inline auto raw_begin() const noexcept -> raw_iterator
 	{
 		return {0, this};
 	}
 
-	inline auto end() noexcept -> iterator
+	inline auto end() const noexcept -> iterator
 	{
 		return {(difference_type) size(), this};
 	}
@@ -569,7 +569,7 @@
 
 
 	/* For doctest stringify */
-	friend std::ostream &operator<<(std::ostream &os, const CharT &value)
+	friend std::ostream &operator<<(std::ostream &os, const basic_mime_string &value)
 	{
 		os << value.storage;
 		return os;