diff --git a/src/Neon/DiffElem.php b/src/Neon/DiffElem.php
new file mode 100644
index 00000000..9c49852b
--- /dev/null
+++ b/src/Neon/DiffElem.php
@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * This file is part of the Nette Framework (https://nette.org)
+ * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
+ */
+
+declare(strict_types=1);
+
+namespace Nette\Neon;
+
+
+/** @internal */
+final class DiffElem
+{
+	public const TYPE_KEEP = 0;
+	public const TYPE_REMOVE = 1;
+	public const TYPE_ADD = 2;
+
+	/** @var int One of the TYPE_* constants */
+	public $type;
+
+	/** @var ?Node\ArrayItemNode Is null for add operations */
+	public $old;
+
+	/** @var ?Node\ArrayItemNode Is null for remove operations */
+	public $new;
+
+
+	public function __construct(int $type, ?Node\ArrayItemNode $old, ?Node\ArrayItemNode $new)
+	{
+		$this->type = $type;
+		$this->old = $old;
+		$this->new = $new;
+	}
+}
diff --git a/src/Neon/Differ.php b/src/Neon/Differ.php
new file mode 100644
index 00000000..fe028ec7
--- /dev/null
+++ b/src/Neon/Differ.php
@@ -0,0 +1,114 @@
+<?php
+
+/**
+ * This file is part of the Nette Framework (https://nette.org)
+ * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
+ */
+
+declare(strict_types=1);
+
+namespace Nette\Neon;
+
+
+/**
+ * Implements the Myers diff algorithm.
+ *
+ * Myers, Eugene W. "An O (ND) difference algorithm and its variations."
+ * Algorithmica 1.1 (1986): 251-266.
+ *
+ * @internal
+ * @author Nikita Popov
+ */
+final class Differ
+{
+	private $isEqual;
+
+
+	public function __construct(callable $isEqual)
+	{
+		$this->isEqual = $isEqual;
+	}
+
+
+	/**
+	 * Calculates diff from $old to $new.
+	 * @return DiffElem[]
+	 */
+	public function diff(array $old, array $new): array
+	{
+		[$trace, $x, $y] = $this->calculateTrace($old, $new);
+		return $this->extractDiff($trace, $x, $y, $old, $new);
+	}
+
+
+	private function calculateTrace(array $a, array $b): array
+	{
+		$n = \count($a);
+		$m = \count($b);
+		$max = $n + $m;
+		$v = [1 => 0];
+		$trace = [];
+		for ($d = 0; $d <= $max; $d++) {
+			$trace[] = $v;
+			for ($k = -$d; $k <= $d; $k += 2) {
+				if ($k === -$d || ($k !== $d && $v[$k-1] < $v[$k+1])) {
+					$x = $v[$k+1];
+				} else {
+					$x = $v[$k-1] + 1;
+				}
+
+				$y = $x - $k;
+				while ($x < $n && $y < $m && ($this->isEqual)($a[$x], $b[$y])) {
+					$x++;
+					$y++;
+				}
+
+				$v[$k] = $x;
+				if ($x >= $n && $y >= $m) {
+					return [$trace, $x, $y];
+				}
+			}
+		}
+		throw new \Exception('Should not happen');
+	}
+
+
+	private function extractDiff(array $trace, int $x, int $y, array $a, array $b): array
+	{
+		$result = [];
+		for ($d = \count($trace) - 1; $d >= 0; $d--) {
+			$v = $trace[$d];
+			$k = $x - $y;
+
+			if ($k === -$d || ($k !== $d && $v[$k-1] < $v[$k+1])) {
+				$prevK = $k + 1;
+			} else {
+				$prevK = $k - 1;
+			}
+
+			$prevX = $v[$prevK];
+			$prevY = $prevX - $prevK;
+
+			while ($x > $prevX && $y > $prevY) {
+				$result[] = new DiffElem(DiffElem::TYPE_KEEP, $a[$x-1], $b[$y-1]);
+				$x--;
+				$y--;
+			}
+
+			if ($d === 0) {
+				break;
+			}
+
+			while ($x > $prevX) {
+				$result[] = new DiffElem(DiffElem::TYPE_REMOVE, $a[$x-1], null);
+				$x--;
+			}
+
+			while ($y > $prevY) {
+				$result[] = new DiffElem(DiffElem::TYPE_ADD, null, $b[$y-1]);
+				$y--;
+			}
+		}
+		return array_reverse($result);
+	}
+}
diff --git a/src/Neon/Merge.php b/src/Neon/Merge.php
new file mode 100644
index 00000000..0de933a2
--- /dev/null
+++ b/src/Neon/Merge.php
@@ -0,0 +1,144 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Nette\Neon;
+
+use Nette\Neon\Node\ArrayItemNode;
+use Nette\Neon\Node\ArrayNode;
+
+
+/** @internal */
+class Merge
+{
+	/** @var TokenStream */
+	private $tokens;
+
+	/** @var Node */
+	private $node;
+
+	/** @var string[] */
+	private $replacements;
+
+	/** @var string[] */
+	private $appends;
+
+
+	public function __construct(string $input)
+	{
+		$input = str_replace("\r", '', $input);
+		$lexer = new Lexer;
+		$parser = new Parser;
+		$this->tokens = $lexer->tokenize($input);
+		$this->node = $parser->parse($this->tokens);
+	}
+
+
+	public function merge($val): string
+	{
+		/*
+		normalization must take place and this notation must be removed:
+
+		- a:
+		  b:
+
+		a:
+		- a
+		- b
+		*/
+
+		$this->replacements = $this->appends = [];
+		$encoder = new Encoder;
+		$newNode = $encoder->valueToNode($val);
+		$this->replaceNode($this->node, $newNode);
+		$res = '';
+		foreach ($this->tokens->getTokens() as $i => $token) {
+			$res .= $this->appends[$i] ?? '';
+			$res .= $this->replacements[$i] ?? $token->value;
+		}
+		return $res;
+	}
+
+
+	private function replaceNode(Node $oldNode, Node $newNode, bool $blockMode = false): void
+	{
+		if ($oldNode->toValue() === $newNode->toValue()) {
+			return;
+
+		} elseif ($oldNode instanceof ArrayNode && $newNode instanceof ArrayNode) {
+			$newNode->indent = $oldNode->indent;
+			if ($oldNode->indent !== null) {
+				$this->replaceArrayItems($oldNode->items, $newNode->items, $oldNode->indent !== null);
+				return;
+			}
+		}
+
+		$newStr = $newNode instanceof ArrayNode && $newNode->indent !== null ? "\n" : '';
+		$newStr .= $newNode->toString();
+		$newStr = rtrim($newStr);
+		$indent = $this->tokens->setPos($oldNode->startPos)->getIndentation();
+		$newStr = self::indent1($newStr, $indent . "\t");
+
+		$this->replaceWith($newStr, $oldNode->startPos, $oldNode->endPos);
+	}
+
+
+	/**
+	 * @param  ArrayItemNode[]  $oldItems
+	 * @param  ArrayItemNode[]  $newItems
+	 */
+	private function replaceArrayItems(array $oldItems, array $newItems): void
+	{
+		$differ = new Differ(function (ArrayItemNode $a, ArrayItemNode $b) {
+			if ($a->key || $b->key) {
+				return ($a->key ? $a->key->toValue() : null) === ($b->key ? $b->key->toValue() : null);
+			} else {
+				return $a->value->toValue() === $b->value->toValue();
+			}
+		});
+		$diff = $differ->diff($oldItems, $newItems);
+		$newPos = $this->tokens->skipLeft($oldItems[0]->startPos, Token::WHITESPACE);
+		$indent = $this->tokens->setPos($newPos)->getIndentation();
+
+		foreach ($diff as $elem) {
+			if ($elem->type === $elem::TYPE_REMOVE) {
+				$startPos = $this->tokens->skipLeft($elem->old->startPos, Token::WHITESPACE);
+				$endPos = $this->tokens->skipRight($elem->old->endPos, Token::WHITESPACE, Token::COMMENT);
+				$endPos = $this->tokens->skipRight($endPos, Token::NEWLINE);
+				$this->replaceWith('', $startPos, $endPos);
+
+			} elseif ($elem->type === $elem::TYPE_KEEP) { // keys are same
+				$this->replaceNode($elem->old->value, $elem->new->value);
+				$newPos = $this->tokens->skipRight($elem->old->value->endPos, Token::WHITESPACE, Token::COMMENT);
+				$newPos = $this->tokens->skipRight($newPos, Token::NEWLINE); // jen jednou!
+				$newPos++;
+
+			} elseif ($elem->type === $elem::TYPE_ADD) {
+				$newStr = Node\ArrayItemNode::itemsToBlockString([$elem->new]);
+				$newStr = self::indent($newStr, $indent);
+				@$this->appends[$newPos] .= $newStr;
+			}
+		}
+	}
+
+
+	private function replaceWith(string $new, int $startPos, int $endPos): void
+	{
+		for ($i = $startPos; $i <= $endPos; $i++) {
+			$this->replacements[$i] = $this->replacements[$i] ?? '';
+		}
+		$this->replacements[$startPos] .= $new;
+	}
+
+
+	private static function indent(string $s, string $indentation = "\t"): string
+	{
+		return preg_replace('#^(?=.)#m', $indentation, $s);
+	}
+
+
+	private static function indent1(string $s, string $indentation = "\t"): string
+	{
+		return str_replace("\n", "\n" . $indentation, $s);
+	}
+}
diff --git a/src/Neon/TokenStream.php b/src/Neon/TokenStream.php
index b30d046c..95e8e309 100644
--- a/src/Neon/TokenStream.php
+++ b/src/Neon/TokenStream.php
@@ -26,6 +26,13 @@ public function __construct(array $tokens)
 	}
 
 
+	public function setPos(int $pos): self
+	{
+		$this->pos = $pos;
+		return $this;
+	}
+
+
 	public function getPos(): int
 	{
 		return $this->pos;
@@ -39,6 +46,24 @@ public function getTokens(): array
 	}
 
 
+	public function skipLeft(int $pos, ...$types): int
+	{
+		while (in_array($this->tokens[$pos - 1]->type ?? null, $types, true)) {
+			$pos--;
+		}
+		return $pos;
+	}
+
+
+	public function skipRight(int $pos, ...$types): int
+	{
+		while (in_array($this->tokens[$pos + 1]->type ?? null, $types, true)) {
+			$pos++;
+		}
+		return $pos;
+	}
+
+
 	public function isNext(...$types): bool
 	{
 		while (in_array($this->tokens[$this->pos]->type ?? null, [Token::COMMENT, Token::WHITESPACE], true)) {
diff --git a/tests/Neon/Merge.phpt b/tests/Neon/Merge.phpt
new file mode 100644
index 00000000..046afa75
--- /dev/null
+++ b/tests/Neon/Merge.phpt
@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+
+include __DIR__ . '/../../vendor/autoload.php';
+
+
+$a = '
+# ahoj
+	ent: ent(  #xxx
+		10,
+		20,
+	)
+	chain: aa(10,20)bb(x)cc
+# world
+';
+
+$b = '
+ent: exnt(
+		10,
+		30,
+	)
+chain: aa(10,20)bbx(x)cc
+fourth:
+';
+
+/*
+$a = '
+next:
+	- [k,
+		l, m, n]
+';
+
+$b = '
+next:
+	- [k, l, ]
+';
+/*
+$a = '
+# ahoj
+first: # first comment
+	# another comment
+	- a  # a comment
+	- b
+	- c
+next:
+	- [k,
+		l, m, n]
+second:
+	sub:
+		a: 1
+		b: 2
+third:
+	x: y
+# world
+';
+
+$b = '
+first:
+	- x
+	- b
+next:
+	- [k, l, ]
+second:
+	sub:
+		a: 5
+		b: 2
+	new: 3
+fourth:
+';
+*/
+
+
+\Tracy\Debugger::$maxDepth = 20;
+\Tracy\Debugger::$dumpTheme = 'dark';
+\Tracy\Debugger::$productionMode = false;
+\Tracy\Debugger::enable();
+
+dump($a);
+dump($b);
+
+$merge = new Nette\Neon\Merge($a);
+$b2 = Nette\Neon\Neon::decode($b);
+dump( $merge->merge($b2) );
+
+$b2 = Nette\Neon\Neon::decode($b);