diff --git a/internal/cgen/base/io-private.h b/internal/cgen/base/io-private.h
index 4802c91..1894934 100644
--- a/internal/cgen/base/io-private.h
+++ b/internal/cgen/base/io-private.h
@@ -227,28 +227,6 @@
   return ret;
 }
 
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_reader__set_limit(wuffs_base__io_reader* o,
-                                 uint8_t* iop_r,
-                                 uint64_t limit) {
-  if (o && (((size_t)(o->private_impl.limit - iop_r)) > limit)) {
-    o->private_impl.limit = iop_r + limit;
-  }
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_reader__set_mark(wuffs_base__io_reader* o, uint8_t* mark) {
-  o->private_impl.mark = mark;
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
 static inline wuffs_base__slice_u8  //
 wuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {
   if (n <= ((size_t)(io1_r - *ptr_iop_r))) {
@@ -282,15 +260,6 @@
   return ret;
 }
 
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_writer__set_mark(wuffs_base__io_writer* o, uint8_t* mark) {
-  o->private_impl.mark = mark;
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
 // ---------------- I/O (Utility)
 
 #define wuffs_base__utility__null_io_reader wuffs_base__null_io_reader
diff --git a/internal/cgen/builtin.go b/internal/cgen/builtin.go
index 9276a38..a59f28b 100644
--- a/internal/cgen/builtin.go
+++ b/internal/cgen/builtin.go
@@ -120,15 +120,6 @@
 		}
 		b.printf("((uint64_t)(%s - %s))", p0, p1)
 		return nil
-
-	case t.IDSet:
-		typ, v := "reader", "r"
-		if len(args) == 1 {
-			typ, v = "writer", "w"
-		}
-		b.printf("wuffs_base__io_%s__set(&v_%s, &u_%s, &iop_v_%s, &io1_v_%s,", typ, v, v, v, v)
-		return g.writeArgs(b, args, depth)
-
 	}
 	return errNoSuchBuiltin
 }
@@ -167,15 +158,6 @@
 			"a_src.private_impl.buf->meta.pos, ((uint64_t)(iop_a_src - a_src.private_impl.buf->data.ptr))) : 0)")
 		return nil
 
-	case t.IDSetLimit:
-		b.printf("wuffs_base__io_reader__set_limit(&%ssrc, iop_a_src,", aPrefix)
-		// TODO: update the iop variables?
-		return g.writeArgs(b, args, depth)
-
-	case t.IDSetMark:
-		b.printf("wuffs_base__io_reader__set_mark(&%ssrc, iop_a_src)", aPrefix)
-		return nil
-
 	case t.IDSince:
 		b.printf("(%s%s.private_impl.buf ? wuffs_base__io__since(", prefix, name)
 		if err := g.writeExpr(b, args[0].AsArg().Value(), depth); err != nil {
@@ -186,16 +168,6 @@
 			prefix, name, prefix, name, prefix, name)
 		return nil
 
-	case t.IDSinceMark, t.IDSinceMarkLength:
-		if method == t.IDSinceMark {
-			b.printf("wuffs_base__make_slice_u8(%s%s.private_impl.mark, (size_t)(", prefix, name)
-		}
-		b.printf("iop_%s%s - %s%s.private_impl.mark", prefix, name, prefix, name)
-		if method == t.IDSinceMark {
-			b.writes("))")
-		}
-		return nil
-
 	case t.IDSkipFast:
 		// Generate a two part expression using the comma operator: "(pointer
 		// increment, return_empty_struct call)". The final part is a function
@@ -294,14 +266,6 @@
 			"a_dst.private_impl.buf->meta.pos, iop_a_dst - a_dst.private_impl.buf->data.ptr) : 0)")
 		return nil
 
-	case t.IDSetMark:
-		// TODO: is a private_impl.mark the right representation? What
-		// if the function is passed a (ptr io_writer) instead of a
-		// (io_writer)? Do we still want to have that mark live outside of
-		// the function scope?
-		b.printf("wuffs_base__io_writer__set_mark(&%sdst, iop_a_dst)", aPrefix)
-		return nil
-
 	case t.IDSince:
 		b.printf("(a_dst.private_impl.buf ? wuffs_base__io__since(")
 		if err := g.writeExpr(b, args[0].AsArg().Value(), depth); err != nil {
@@ -309,16 +273,6 @@
 		}
 		b.printf(", iop_a_dst - a_dst.private_impl.buf->data.ptr, a_dst.private_impl.buf->data.ptr) : wuffs_base__make_slice_u8(NULL, 0))")
 		return nil
-
-	case t.IDSinceMark, t.IDSinceMarkLength:
-		if method == t.IDSinceMark {
-			b.printf("wuffs_base__make_slice_u8(%s%s.private_impl.mark, (size_t)(", prefix, name)
-		}
-		b.printf("iop_%s%s - %s%s.private_impl.mark", prefix, name, prefix, name)
-		if method == t.IDSinceMark {
-			b.writes("))")
-		}
-		return nil
 	}
 
 	if method >= writeFastMethodsBase {
@@ -448,25 +402,6 @@
 		return g.writeArgs(b, args, depth)
 
 	case t.IDLength:
-		if recv.Operator() == t.IDOpenParen {
-			if method := recv.LHS().AsExpr(); method.Operator() == t.IDDot && method.Ident() == t.IDSinceMark {
-				if lhs := method.LHS().AsExpr(); lhs.MType().IsIOType() {
-					b.writes("((uint64_t)(")
-					if lhs.MType().QID()[1] == t.IDIOReader {
-						if err := g.writeBuiltinIOReader(b, lhs, t.IDSinceMarkLength, nil, depth); err != nil {
-							return err
-						}
-					} else {
-						if err := g.writeBuiltinIOWriter(b, lhs, t.IDSinceMarkLength, nil, depth); err != nil {
-							return err
-						}
-					}
-					b.writes("))")
-					return nil
-				}
-			}
-		}
-
 		b.writes("((uint64_t)(")
 		if err := g.writeExpr(b, recv, depth); err != nil {
 			return err
diff --git a/internal/cgen/data.go b/internal/cgen/data.go
index 621cbd6..dd3d0cd 100644
--- a/internal/cgen/data.go
+++ b/internal/cgen/data.go
@@ -169,9 +169,8 @@
 	" but that\n  // is mostly because 3 is the minimum length for the deflate format. This\n  // function implementation shouldn't overfit to that one format. Perhaps the\n  // copy_n_from_history Wuffs method should also take an unroll hint argument,\n  // and the cgen can look if that argument is the constant expression '3'.\n  //\n  // See also wuffs_base__io_writer__copy_n_from_history_fast below.\n  //\n  // Alternatively, or additionally, have a sloppy_copy_n_from_history method\n  // that copies 8 bytes at a time, possibly writing more than length bytes?\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\n// wuffs_base__io_writer__copy_n_from_history_fast is like the\n// wuffs_base__io_writer__copy_n_from_history function above, but has stronger\n// pre-conditions. The caller needs to prove that:\n//  - distance >  0\n//  - distance <= (*ptr_iop_w - io0_w)\n//  - length   <= (io1_w      - *ptr_iop_w)\nstatic inline" +
 	" uint32_t  //\nwuffs_base__io_writer__copy_n_from_history_fast(uint8_t** ptr_iop_w,\n                                                uint8_t* io0_w,\n                                                uint8_t* io1_w,\n                                                uint32_t length,\n                                                uint32_t distance) {\n  uint8_t* p = *ptr_iop_w;\n  uint8_t* q = p - distance;\n  uint32_t n = length;\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_reader(uint8_t** ptr_iop_w,\n                                          uint8_t* io1_w,\n                                          uint32_t length,\n                                          uint8_t** ptr_iop_r,\n                                          uint8_t* io1_r) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = length;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io" +
 	"1_w - iop_w);\n  }\n  uint8_t* iop_r = *ptr_iop_r;\n  if (n > ((size_t)(io1_r - iop_r))) {\n    n = (size_t)(io1_r - iop_r);\n  }\n  if (n > 0) {\n    memmove(iop_w, iop_r, n);\n    *ptr_iop_w += n;\n    *ptr_iop_r += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline uint64_t  //\nwuffs_base__io_writer__copy_from_slice(uint8_t** ptr_iop_w,\n                                       uint8_t* io1_w,\n                                       wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint64_t)(n);\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_slice(uint8_t** ptr_iop_w,\n                                         uint8_t* io1_w,\n                                         uint32_t length,\n                                         wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > length) " +
-	"{\n    n = length;\n  }\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set(wuffs_base__io_reader* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_r,\n                           uint8_t** ptr_io1_r,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = data.len;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_r = data.ptr;\n  *ptr_io1_r = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set_limit(wuffs_base__io_reader* o,\n                                 uint8_t* iop_r,\n                        " +
-	"         uint64_t limit) {\n  if (o && (((size_t)(o->private_impl.limit - iop_r)) > limit)) {\n    o->private_impl.limit = iop_r + limit;\n  }\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set_mark(wuffs_base__io_reader* o, uint8_t* mark) {\n  o->private_impl.mark = mark;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {\n  if (n <= ((size_t)(io1_r - *ptr_iop_r))) {\n    uint8_t* p = *ptr_iop_r;\n    *ptr_iop_r += n;\n    return wuffs_base__make_slice_u8(p, n);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_writer__set(wuffs_base__io_writer* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_w,\n                           uint8_t** ptr_io1_w,\n                           wuffs_" +
-	"base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = 0;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_w = data.ptr;\n  *ptr_io1_w = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_writer__set_mark(wuffs_base__io_writer* o, uint8_t* mark) {\n  o->private_impl.mark = mark;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\n" +
+	"{\n    n = length;\n  }\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set(wuffs_base__io_reader* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_r,\n                           uint8_t** ptr_io1_r,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = data.len;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_r = data.ptr;\n  *ptr_io1_r = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {\n  if (n <= ((size_t)(io1_r - *ptr_iop_r))) {\n    uint8_t*" +
+	" p = *ptr_iop_r;\n    *ptr_iop_r += n;\n    return wuffs_base__make_slice_u8(p, n);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_writer__set(wuffs_base__io_writer* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_w,\n                           uint8_t** ptr_io1_w,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = 0;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_w = data.ptr;\n  *ptr_io1_w = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\n" +
 	"" +
 	"// ---------------- I/O (Utility)\n\n#define wuffs_base__utility__null_io_reader wuffs_base__null_io_reader\n#define wuffs_base__utility__null_io_writer wuffs_base__null_io_writer\n" +
 	""
diff --git a/lang/builtin/builtin.go b/lang/builtin/builtin.go
index 25ab7c7..919fe86 100644
--- a/lang/builtin/builtin.go
+++ b/lang/builtin/builtin.go
@@ -220,11 +220,7 @@
 	"io_reader.count_since(mark u64) u64",
 	"io_reader.mark() u64",
 	"io_reader.position() u64",
-	"io_reader.set!(s slice u8, closed bool)", // TODO: remove, as it's no longer used?
-	"io_reader.set_limit!(l u64)",             // TODO: remove, as it's no longer used?
-	"io_reader.set_mark!()",
 	"io_reader.since(mark u64) slice u8",
-	"io_reader.since_mark() slice u8",
 	"io_reader.take!(n u64) slice u8",
 
 	"io_reader.skip?(n u32)",
@@ -279,11 +275,7 @@
 	"io_writer.history_available() u64",
 	"io_writer.mark() u64",
 	"io_writer.position() u64",
-	"io_writer.set!(s slice u8)",  // TODO: remove, as it's no longer used?
-	"io_writer.set_limit!(l u64)", // TODO: remove, as it's no longer used?
-	"io_writer.set_mark!()",
 	"io_writer.since(mark u64) slice u8",
-	"io_writer.since_mark() slice u8",
 
 	"io_writer.copy_from_slice!(s slice u8) u64",
 	"io_writer.copy_n_from_history!(n u32, distance u32) u32",
diff --git a/lang/token/list.go b/lang/token/list.go
index 53756ba..765ef80 100644
--- a/lang/token/list.go
+++ b/lang/token/list.go
@@ -464,14 +464,10 @@
 	IDHistoryAvailable = ID(0x162)
 	IDMark             = ID(0x163)
 	IDPosition         = ID(0x164)
-	IDSetLimit         = ID(0x165)
-	IDSetMark          = ID(0x166)
-	IDSince            = ID(0x167)
-	IDSinceMark        = ID(0x168)
-	IDSinceMarkLength  = ID(0x169)
-	IDSkip             = ID(0x16A)
-	IDSkipFast         = ID(0x16B)
-	IDTake             = ID(0x16C)
+	IDSince            = ID(0x165)
+	IDSkip             = ID(0x166)
+	IDSkipFast         = ID(0x167)
+	IDTake             = ID(0x168)
 
 	IDCopyFromSlice        = ID(0x170)
 	IDCopyNFromHistory     = ID(0x171)
@@ -800,11 +796,7 @@
 	IDHistoryAvailable: "history_available",
 	IDMark:             "mark",
 	IDPosition:         "position",
-	IDSetLimit:         "set_limit",
-	IDSetMark:          "set_mark",
 	IDSince:            "since",
-	IDSinceMark:        "since_mark",
-	IDSinceMarkLength:  "since_mark_length",
 	IDSkip:             "skip",
 	IDSkipFast:         "skip_fast",
 	IDTake:             "take",
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 41ab2b0..703f0f2 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -4731,28 +4731,6 @@
   return ret;
 }
 
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_reader__set_limit(wuffs_base__io_reader* o,
-                                 uint8_t* iop_r,
-                                 uint64_t limit) {
-  if (o && (((size_t)(o->private_impl.limit - iop_r)) > limit)) {
-    o->private_impl.limit = iop_r + limit;
-  }
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_reader__set_mark(wuffs_base__io_reader* o, uint8_t* mark) {
-  o->private_impl.mark = mark;
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
 static inline wuffs_base__slice_u8  //
 wuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {
   if (n <= ((size_t)(io1_r - *ptr_iop_r))) {
@@ -4786,15 +4764,6 @@
   return ret;
 }
 
-static inline wuffs_base__empty_struct  //
-wuffs_base__io_writer__set_mark(wuffs_base__io_writer* o, uint8_t* mark) {
-  o->private_impl.mark = mark;
-
-  wuffs_base__empty_struct ret;
-  ret.private_impl = 0;
-  return ret;
-}
-
   // ---------------- I/O (Utility)
 
 #define wuffs_base__utility__null_io_reader wuffs_base__null_io_reader