diff --git a/CHANGELOG.md b/CHANGELOG.md
index b586211..7cda0fc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -130,6 +130,23 @@ All notable changes to this project are documented here. The format follows
 
 ### Changed
 
+- **The install says which plugin, and what happens without it.** The requirement named
+  "a plugin" and the plugin two sentences later, so a consumer who stopped at the
+  requirement did not know what to allow. The README names
+  [`cweagans/composer-patches`][composer-patches] where the requirement is stated now,
+  and says what follows: the install stops with Composer's own message naming the
+  plugin, and a conversion against an unpatched PHPPresentation raises
+  `MarkdownPresentation\Exception\UnpatchedDependency`, whose message names the plugin
+  as well.
+
+  The page names the five methods [the patch][the-patch] adds and says which direction
+  needs each: the writer — the direction that writes a deck — needs
+  `Table::setFirstRow`, `AutoShape::setRoundRectCorner` and `RichText::setDescription`,
+  and the reader — the direction that takes a deck apart, through the patched
+  `PowerPoint2007` reader — needs `PowerPoint2007::zipPath` and `Gd::setContents` as well
+  as the description. The check asks for all five whichever way the library is used, and a
+  package that carries only some of them is refused rather than half-worked.
+
 - **`PresentationRenderer` is split, and `php:S1448` is closed on it.** Twenty-three
   methods was one finding too many, and the finding says what to do: split it.
 
diff --git a/README.md b/README.md
index 4e07ba6..93a6ec5 100644
--- a/README.md
+++ b/README.md
@@ -33,12 +33,12 @@ PHP 8.2 or newer, `symfony/yaml` and `phpoffice/phppresentation` as hard depende
 frontmatter of a deck and every file of a theme is YAML, and a partial parser is worse for
 the machines that write them than for the people that do.
 
-**The project that installs this one has to allow a plugin.** This library writes a few
-things a released PHPPresentation cannot — a table that says which row is its header, a
-shape that says how round its corners are, a picture that says where it was read from — and
-gets them from a patch applied to the installed package. The patch is applied by
-[`cweagans/composer-patches`][composer-patches], which Composer only runs when the project
-allows it:
+**The project that installs this one has to allow [`cweagans/composer-patches`][composer-patches].**
+This library writes a few things a released PHPPresentation cannot — a table that says which
+row is its header, a shape that says how round its corners are, a run of text that says what
+it is, and a picture that says where it was read from — and gets them from a patch applied to
+the installed package. The plugin applies that patch, and Composer runs it only when the
+project allows it:
 
 ```json
 {
@@ -50,9 +50,26 @@ allows it:
 }
 ```
 
-Without that line the install stops with Composer's own message naming the plugin. The
-library refuses to work rather than write a deck with the parts missing, and says which
-plugin is the reason.
+Without that line the install stops with Composer's own message naming
+`cweagans/composer-patches`. A deck converted against an unpatched PHPPresentation raises
+`MarkdownPresentation\Exception\UnpatchedDependency`, whose message names the plugin as
+well.
+
+The patch adds five methods to PHPPresentation:
+
+| Method | Needed by | What it is for |
+| --- | --- | --- |
+| `Table::setFirstRow` | the writer | whether the first row of a table is its header |
+| `AutoShape::setRoundRectCorner` | the writer | how round the corners of a rounded rectangle are |
+| `RichText::setDescription` | the writer and the reader | the description a shape carries: the writer sets it, the reader reads it back |
+| `PowerPoint2007::zipPath` | the reader | the path a picture was read from, inside the package |
+| `Gd::setContents` | the reader | the bytes a picture was read from, as the package holds them |
+
+The writer is the direction that writes a `.pptx`; the reader is the direction that takes one
+apart, and it reads a deck through the patched `PowerPoint2007` reader. The check asks for
+all five of them, in either direction, and a package that carries only some is refused
+rather than half-worked. What is missing either fails somewhere else — naming a method
+rather than the reason — or is quietly left out of the deck that comes back.
 
 `ext-imagick` is optional and enables [SVG](#what-an-svg-costs-you). PowerPoint holds a
 vector only beside a raster of it, so something has to draw the raster; without the
diff --git a/tests/Readme/installation.php b/tests/Readme/installation.php
index 367b8a6..ee37116 100644
--- a/tests/Readme/installation.php
+++ b/tests/Readme/installation.php
@@ -20,6 +20,12 @@
  * rather than the other way round: when the patch goes, and the pin becomes a release
  * that carries the fixes on its own, the line stops being asked for and the guard says
  * so.
+ *
+ * The rest of the section says what the plugin is for, and a consumer who has to
+ * find that out from the failure is a consumer who has been told too late: the
+ * requirement names the plugin, the consequence names it again, and the methods the
+ * patch adds are read out of the class that checks for them — so a patch that grows a
+ * method makes the page a list of the methods there are.
  */
 
 /**
@@ -44,6 +50,84 @@ function installationManifest(): array
     );
 }
 
+/**
+ * The installation section, as it is on the page.
+ */
+function installationSection(): string
+{
+    $readme = installationReadme();
+
+    return preg_match('~^## Installation$(.*?)^## ~ms', $readme, $section) === 1 ? $section[1] : '';
+}
+
+/**
+ * The paragraphs of the installation section, as they are on the page.
+ *
+ * @return list<string>
+ */
+function installationParagraphs(): array
+{
+    $paragraphs = [];
+
+    foreach (preg_split('#\n\s*\n#', installationSection()) ?: [] as $paragraph) {
+        $paragraph = trim($paragraph);
+
+        if ($paragraph !== '') {
+            $paragraphs[] = $paragraph;
+        }
+    }
+
+    return $paragraphs;
+}
+
+/**
+ * The sentence that states the requirement.
+ *
+ * The sentence rather than the paragraph, because the paragraph says more than the
+ * requirement does: a plugin named two sentences later is not named where the
+ * requirement is stated.
+ */
+function installationRequirement(): string
+{
+    $section = installationSection();
+    $at = strpos($section, 'has to allow');
+
+    if ($at === false) {
+        return '';
+    }
+
+    $end = strpos($section, '.', $at);
+
+    return $end === false ? substr($section, $at) : substr($section, $at, $end - $at);
+}
+
+/**
+ * The methods the library requires from the installed PHPPresentation.
+ *
+ * Read out of the class that checks for them rather than written down here, so that
+ * a patch which grows a method makes the page a list of the methods there are.
+ *
+ * @return array<class-string, string> The class each method belongs to, and the method.
+ */
+function requiredFixes(): array
+{
+    $required = (new ReflectionClass(\MarkdownPresentation\Fixes::class))->getConstant('REQUIRED');
+
+    if (! is_array($required)) {
+        return [];
+    }
+
+    $fixes = [];
+
+    foreach ($required as $class => $method) {
+        if (is_string($class) && is_string($method) && class_exists($class)) {
+            $fixes[$class] = $method;
+        }
+    }
+
+    return $fixes;
+}
+
 it('asks a consumer for the plugin that applies the patch', function () {
     $manifest = installationManifest();
     $patches = $manifest['extra']['patches'] ?? [];
@@ -67,3 +151,48 @@ function installationManifest(): array
     expect(installationReadme())->not->toContain('minimum-stability');
     expect($needsIt)->toBeFalse();
 });
+
+it('names the plugin where the requirement is stated', function () {
+    // The sentence that says the project has to allow the plugin is the sentence a
+    // consumer stops at, so the plugin is named in it rather than a sentence later.
+    $requirement = installationRequirement();
+
+    expect($requirement)->not->toBe('');
+    expect($requirement)->toContain('cweagans/composer-patches');
+});
+
+it('states what a consumer gets without the plugin', function () {
+    $readme = installationReadme();
+
+    // Two failures, and a consumer meets the first at the install and the second at
+    // the render: the install stops with Composer's own message, and a conversion
+    // against an unpatched package raises the library's own.
+    expect($readme)->toContain('the install stops');
+
+    $consequences = array_values(array_filter(
+        installationParagraphs(),
+        static fn (string $paragraph): bool => str_contains($paragraph, 'UnpatchedDependency'),
+    ));
+
+    expect($consequences)->toHaveCount(1);
+    expect($consequences[0])->toContain('cweagans/composer-patches');
+});
+
+it('names every method the library requires', function () {
+    $fixes = requiredFixes();
+
+    expect($fixes)->not->toBe([]);
+
+    $readme = installationReadme();
+    $missing = [];
+
+    foreach ($fixes as $class => $method) {
+        $named = (new ReflectionClass($class))->getShortName() . '::' . $method;
+
+        if (! str_contains($readme, $named)) {
+            $missing[] = $named;
+        }
+    }
+
+    expect($missing)->toBe([]);
+});