diff --git a/css/css-animations/parsing/animation-trigger-exit-range-end-computed.html b/css/css-animations/parsing/animation-trigger-exit-range-end-computed.html
new file mode 100644
index 00000000000000..d2baab5b2a5c23
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-end-computed.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<div id="target" style="font-size:10px;"></div>
+<script>
+test_computed_value("animation-trigger-exit-range-end", "initial", "normal");
+test_computed_value("animation-trigger-exit-range-end", "normal");
+test_computed_value("animation-trigger-exit-range-end", "cover 0%");
+test_computed_value("animation-trigger-exit-range-end", "cover 100%", "cover");
+test_computed_value("animation-trigger-exit-range-end", "COVER 0%", "cover 0%");
+test_computed_value("animation-trigger-exit-range-end", "COVER 100%", "cover");
+test_computed_value("animation-trigger-exit-range-end", "cover 120%");
+test_computed_value("animation-trigger-exit-range-end", "0", "0px");
+test_computed_value("animation-trigger-exit-range-end", "120%");
+test_computed_value("animation-trigger-exit-range-end", "120px");
+test_computed_value("animation-trigger-exit-range-end", "cover 42%");
+test_computed_value("animation-trigger-exit-range-end", "cover -42%");
+test_computed_value("animation-trigger-exit-range-end", "contain 42%");
+test_computed_value("animation-trigger-exit-range-end", "exit 42%");
+test_computed_value("animation-trigger-exit-range-end", "exit calc(41% + 1%)", "exit 42%");
+test_computed_value("animation-trigger-exit-range-end", "exit-crossing 42%");
+test_computed_value("animation-trigger-exit-range-end", "exit 1%, cover 2%, contain 0%");
+test_computed_value("animation-trigger-exit-range-end", "exit 1%, cover 2%, contain 100%", "exit 1%, cover 2%, contain");
+test_computed_value("animation-trigger-exit-range-end", "entry 42px");
+test_computed_value("animation-trigger-exit-range-end", "entry-crossing 42px");
+
+test_computed_value("animation-trigger-exit-range-end", "contain calc(10% + 10px)");
+test_computed_value("animation-trigger-exit-range-end", "entry 1em", "entry 10px");
+test_computed_value("animation-trigger-exit-range-end", "exit calc(1em + 10px)", "exit 20px");
+test_computed_value("animation-trigger-exit-range-end", "cover");
+test_computed_value("animation-trigger-exit-range-end", "contain");
+test_computed_value("animation-trigger-exit-range-end", "entry");
+test_computed_value("animation-trigger-exit-range-end", "exit");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-exit-range-end-invalid.html b/css/css-animations/parsing/animation-trigger-exit-range-end-invalid.html
new file mode 100644
index 00000000000000..111847151ef6c0
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-end-invalid.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+test_invalid_value("animation-trigger-exit-range-end", "infinite");
+test_invalid_value("animation-trigger-exit-range-end", "1s 2s");
+test_invalid_value("animation-trigger-exit-range-end", "1s / 2s");
+
+test_invalid_value("animation-trigger-exit-range-end", "peek 50%");
+test_invalid_value("animation-trigger-exit-range-end", "50% contain");
+test_invalid_value("animation-trigger-exit-range-end", "50% cover");
+test_invalid_value("animation-trigger-exit-range-end", "50% entry");
+test_invalid_value("animation-trigger-exit-range-end", "50% enter");
+test_invalid_value("animation-trigger-exit-range-end", "50% exit");
+test_invalid_value("animation-trigger-exit-range-end", "contain contain");
+test_invalid_value("animation-trigger-exit-range-end", "none");
+test_invalid_value("animation-trigger-exit-range-end", "cover 50% enter 50%");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-exit-range-end-valid.html b/css/css-animations/parsing/animation-trigger-exit-range-end-valid.html
new file mode 100644
index 00000000000000..9a41889d3396de
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-end-valid.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+// https://drafts.csswg.org/scroll-animations-1/#view-timelines-ranges
+test_valid_value("animation-trigger-exit-range-end", "normal");
+test_valid_value("animation-trigger-exit-range-end", "cover 0%");
+test_valid_value("animation-trigger-exit-range-end", "cover 100%", "cover");
+test_valid_value("animation-trigger-exit-range-end", "cover 120%");
+test_valid_value("animation-trigger-exit-range-end", "cover 42%");
+test_valid_value("animation-trigger-exit-range-end", "0", "0px");
+test_valid_value("animation-trigger-exit-range-end", "120%");
+test_valid_value("animation-trigger-exit-range-end", "120px");
+test_valid_value("animation-trigger-exit-range-end", "cover -42%");
+test_valid_value("animation-trigger-exit-range-end", "contain 42%");
+test_valid_value("animation-trigger-exit-range-end", "exit 42%");
+test_valid_value("animation-trigger-exit-range-end", "exit 1%, cover 2%, contain 0%");
+test_valid_value("animation-trigger-exit-range-end", "exit 1%, cover 2%, contain 100%", "exit 1%, cover 2%, contain");
+test_valid_value("animation-trigger-exit-range-end", "exit-crossing 42%");
+test_valid_value("animation-trigger-exit-range-end", "entry 42px");
+test_valid_value("animation-trigger-exit-range-end", "entry-crossing 42px");
+test_valid_value("animation-trigger-exit-range-end", "contain calc(10px + 10%)", "contain calc(10% + 10px)");
+test_valid_value("animation-trigger-exit-range-end", "entry 1em");
+test_valid_value("animation-trigger-exit-range-end", "exit calc(1em + 10px)");
+test_valid_value("animation-trigger-exit-range-end", "entry 42%");
+test_valid_value("animation-trigger-exit-range-end", "cover");
+test_valid_value("animation-trigger-exit-range-end", "contain");
+test_valid_value("animation-trigger-exit-range-end", "entry");
+test_valid_value("animation-trigger-exit-range-end", "exit");
+</script>trigger-
diff --git a/css/css-animations/parsing/animation-trigger-exit-range-start-computed.html b/css/css-animations/parsing/animation-trigger-exit-range-start-computed.html
new file mode 100644
index 00000000000000..a48e15a578dcbb
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-start-computed.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<div id="target" style="font-size:10px;"></div>
+<script>
+test_computed_value("animation-trigger-exit-range-start", "initial", "normal");
+test_computed_value("animation-trigger-exit-range-start", "normal");
+test_computed_value("animation-trigger-exit-range-start", "cover 0%", "cover");
+test_computed_value("animation-trigger-exit-range-start", "cover 100%");
+test_computed_value("animation-trigger-exit-range-start", "COVER 0%", "cover");
+test_computed_value("animation-trigger-exit-range-start", "COVER 100%", "cover 100%");
+test_computed_value("animation-trigger-exit-range-start", "cover 120%");
+test_computed_value("animation-trigger-exit-range-start", "cover 42%");
+test_computed_value("animation-trigger-exit-range-start", "0", "0px");
+test_computed_value("animation-trigger-exit-range-start", "120%");
+test_computed_value("animation-trigger-exit-range-start", "120px");
+test_computed_value("animation-trigger-exit-range-start", "cover -42%");
+test_computed_value("animation-trigger-exit-range-start", "contain 42%");
+test_computed_value("animation-trigger-exit-range-start", "exit 42%");
+test_computed_value("animation-trigger-exit-range-start", "exit calc(41% + 1%)", "exit 42%");
+test_computed_value("animation-trigger-exit-range-start", "exit 1%, cover 2%, contain 0%", "exit 1%, cover 2%, contain");
+test_computed_value("animation-trigger-exit-range-start", "exit 1%, cover 2%, contain 100%");
+test_computed_value("animation-trigger-exit-range-start", "exit-crossing 42%");
+test_computed_value("animation-trigger-exit-range-start", "entry 42px");
+test_computed_value("animation-trigger-exit-range-start", "entry-crossing 42px");
+test_computed_value("animation-trigger-exit-range-start", "contain calc(10% + 10px)");
+test_computed_value("animation-trigger-exit-range-start", "entry 1em", "entry 10px");
+test_computed_value("animation-trigger-exit-range-start", "exit calc(1em + 10px)", "exit 20px");
+test_computed_value("animation-trigger-exit-range-start", "cover");
+test_computed_value("animation-trigger-exit-range-start", "contain");
+test_computed_value("animation-trigger-exit-range-start", "entry");
+test_computed_value("animation-trigger-exit-range-start", "exit");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-exit-range-start-invalid.html b/css/css-animations/parsing/animation-trigger-exit-range-start-invalid.html
new file mode 100644
index 00000000000000..220b8028dd312e
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-start-invalid.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+test_invalid_value("animation-trigger-exit-range-start", "peek 50%");
+test_invalid_value("animation-trigger-exit-range-start", "50% contain");
+test_invalid_value("animation-trigger-exit-range-start", "50% cover");
+test_invalid_value("animation-trigger-exit-range-start", "50% entry");
+test_invalid_value("animation-trigger-exit-range-start", "50% enter");
+test_invalid_value("animation-trigger-exit-range-start", "50% exit");
+test_invalid_value("animation-trigger-exit-range-start", "contain contain");
+test_invalid_value("animation-trigger-exit-range-start", "none");
+test_invalid_value("animation-trigger-exit-range-start", "cover 50% enter 50%");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-exit-range-start-valid.html b/css/css-animations/parsing/animation-trigger-exit-range-start-valid.html
new file mode 100644
index 00000000000000..11d1adb26f8983
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-exit-range-start-valid.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+// https://drafts.csswg.org/scroll-animations-1/#view-timelines-ranges
+test_valid_value("animation-trigger-exit-range-start", "normal");
+test_valid_value("animation-trigger-exit-range-start", "cover 0%", "cover");
+test_valid_value("animation-trigger-exit-range-start", "cover 100%");
+test_valid_value("animation-trigger-exit-range-start", "cover 120%");
+test_valid_value("animation-trigger-exit-range-start", "cover 42%");
+test_valid_value("animation-trigger-exit-range-start", "0", "0px");
+test_valid_value("animation-trigger-exit-range-start", "120%");
+test_valid_value("animation-trigger-exit-range-start", "120px");
+test_valid_value("animation-trigger-exit-range-start", "cover -42%");
+test_valid_value("animation-trigger-exit-range-start", "contain 42%");
+test_valid_value("animation-trigger-exit-range-start", "exit 42%");
+test_valid_value("animation-trigger-exit-range-start", "exit 1%, cover 2%, contain 0%", "exit 1%, cover 2%, contain");
+test_valid_value("animation-trigger-exit-range-start", "exit 1%, cover 2%, contain 100%");
+test_valid_value("animation-trigger-exit-range-start", "exit-crossing 42%");
+test_valid_value("animation-trigger-exit-range-start", "entry 42px");
+test_valid_value("animation-trigger-exit-range-start", "entry-crossing 42px");
+test_valid_value("animation-trigger-exit-range-start", "contain calc(10px + 10%)", "contain calc(10% + 10px)");
+test_valid_value("animation-trigger-exit-range-start", "entry 1em");
+test_valid_value("animation-trigger-exit-range-start", "exit calc(1em + 10px)");
+test_valid_value("animation-trigger-exit-range-start", "entry 42%");
+test_valid_value("animation-trigger-exit-range-start", "cover");
+test_valid_value("animation-trigger-exit-range-start", "contain");
+test_valid_value("animation-trigger-exit-range-start", "entry");
+test_valid_value("animation-trigger-exit-range-start", "exit");
+test_valid_value("animation-trigger-exit-range-start", "cover calc(sign(100em - 1px) * 1%)");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-range-end-computed.html b/css/css-animations/parsing/animation-trigger-range-end-computed.html
new file mode 100644
index 00000000000000..63ee6218f12bdd
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-end-computed.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<div id="target" style="font-size:10px;"></div>
+<script>
+test_computed_value("animation-trigger-range-end", "initial", "normal");
+test_computed_value("animation-trigger-range-end", "normal");
+test_computed_value("animation-trigger-range-end", "cover 0%");
+test_computed_value("animation-trigger-range-end", "cover 100%", "cover");
+test_computed_value("animation-trigger-range-end", "COVER 0%", "cover 0%");
+test_computed_value("animation-trigger-range-end", "COVER 100%", "cover");
+test_computed_value("animation-trigger-range-end", "cover 120%");
+test_computed_value("animation-trigger-range-end", "0", "0px");
+test_computed_value("animation-trigger-range-end", "120%");
+test_computed_value("animation-trigger-range-end", "120px");
+test_computed_value("animation-trigger-range-end", "cover 42%");
+test_computed_value("animation-trigger-range-end", "cover -42%");
+test_computed_value("animation-trigger-range-end", "contain 42%");
+test_computed_value("animation-trigger-range-end", "exit 42%");
+test_computed_value("animation-trigger-range-end", "exit calc(41% + 1%)", "exit 42%");
+test_computed_value("animation-trigger-range-end", "exit-crossing 42%");
+test_computed_value("animation-trigger-range-end", "exit 1%, cover 2%, contain 0%");
+test_computed_value("animation-trigger-range-end", "exit 1%, cover 2%, contain 100%", "exit 1%, cover 2%, contain");
+test_computed_value("animation-trigger-range-end", "entry 42px");
+test_computed_value("animation-trigger-range-end", "entry-crossing 42px");
+
+test_computed_value("animation-trigger-range-end", "contain calc(10% + 10px)");
+test_computed_value("animation-trigger-range-end", "entry 1em", "entry 10px");
+test_computed_value("animation-trigger-range-end", "exit calc(1em + 10px)", "exit 20px");
+test_computed_value("animation-trigger-range-end", "cover");
+test_computed_value("animation-trigger-range-end", "contain");
+test_computed_value("animation-trigger-range-end", "entry");
+test_computed_value("animation-trigger-range-end", "exit");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-range-end-invalid.html b/css/css-animations/parsing/animation-trigger-range-end-invalid.html
new file mode 100644
index 00000000000000..8d66ac661d5434
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-end-invalid.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+test_invalid_value("animation-trigger-range-end", "infinite");
+test_invalid_value("animation-trigger-range-end", "1s 2s");
+test_invalid_value("animation-trigger-range-end", "1s / 2s");
+
+test_invalid_value("animation-trigger-range-end", "peek 50%");
+test_invalid_value("animation-trigger-range-end", "50% contain");
+test_invalid_value("animation-trigger-range-end", "50% cover");
+test_invalid_value("animation-trigger-range-end", "50% entry");
+test_invalid_value("animation-trigger-range-end", "50% enter");
+test_invalid_value("animation-trigger-range-end", "50% exit");
+test_invalid_value("animation-trigger-range-end", "contain contain");
+test_invalid_value("animation-trigger-range-end", "none");
+test_invalid_value("animation-trigger-range-end", "cover 50% enter 50%");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-range-end-valid.html b/css/css-animations/parsing/animation-trigger-range-end-valid.html
new file mode 100644
index 00000000000000..6d9533e2648092
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-end-valid.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+// https://drafts.csswg.org/scroll-animations-1/#view-timelines-ranges
+test_valid_value("animation-trigger-range-end", "normal");
+test_valid_value("animation-trigger-range-end", "cover 0%");
+test_valid_value("animation-trigger-range-end", "cover 100%", "cover");
+test_valid_value("animation-trigger-range-end", "cover 120%");
+test_valid_value("animation-trigger-range-end", "cover 42%");
+test_valid_value("animation-trigger-range-end", "0", "0px");
+test_valid_value("animation-trigger-range-end", "120%");
+test_valid_value("animation-trigger-range-end", "120px");
+test_valid_value("animation-trigger-range-end", "cover -42%");
+test_valid_value("animation-trigger-range-end", "contain 42%");
+test_valid_value("animation-trigger-range-end", "exit 42%");
+test_valid_value("animation-trigger-range-end", "exit 1%, cover 2%, contain 0%");
+test_valid_value("animation-trigger-range-end", "exit 1%, cover 2%, contain 100%", "exit 1%, cover 2%, contain");
+test_valid_value("animation-trigger-range-end", "exit-crossing 42%");
+test_valid_value("animation-trigger-range-end", "entry 42px");
+test_valid_value("animation-trigger-range-end", "entry-crossing 42px");
+test_valid_value("animation-trigger-range-end", "contain calc(10px + 10%)", "contain calc(10% + 10px)");
+test_valid_value("animation-trigger-range-end", "entry 1em");
+test_valid_value("animation-trigger-range-end", "exit calc(1em + 10px)");
+test_valid_value("animation-trigger-range-end", "entry 42%");
+test_valid_value("animation-trigger-range-end", "cover");
+test_valid_value("animation-trigger-range-end", "contain");
+test_valid_value("animation-trigger-range-end", "entry");
+test_valid_value("animation-trigger-range-end", "exit");
+</script>trigger-
diff --git a/css/css-animations/parsing/animation-trigger-range-start-computed.html b/css/css-animations/parsing/animation-trigger-range-start-computed.html
new file mode 100644
index 00000000000000..7b1f9e37e62f74
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-start-computed.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<div id="target" style="font-size:10px;"></div>
+<script>
+test_computed_value("animation-trigger-range-start", "initial", "normal");
+test_computed_value("animation-trigger-range-start", "normal");
+test_computed_value("animation-trigger-range-start", "cover 0%", "cover");
+test_computed_value("animation-trigger-range-start", "cover 100%");
+test_computed_value("animation-trigger-range-start", "COVER 0%", "cover");
+test_computed_value("animation-trigger-range-start", "COVER 100%", "cover 100%");
+test_computed_value("animation-trigger-range-start", "cover 120%");
+test_computed_value("animation-trigger-range-start", "cover 42%");
+test_computed_value("animation-trigger-range-start", "0", "0px");
+test_computed_value("animation-trigger-range-start", "120%");
+test_computed_value("animation-trigger-range-start", "120px");
+test_computed_value("animation-trigger-range-start", "cover -42%");
+test_computed_value("animation-trigger-range-start", "contain 42%");
+test_computed_value("animation-trigger-range-start", "exit 42%");
+test_computed_value("animation-trigger-range-start", "exit calc(41% + 1%)", "exit 42%");
+test_computed_value("animation-trigger-range-start", "exit 1%, cover 2%, contain 0%", "exit 1%, cover 2%, contain");
+test_computed_value("animation-trigger-range-start", "exit 1%, cover 2%, contain 100%");
+test_computed_value("animation-trigger-range-start", "exit-crossing 42%");
+test_computed_value("animation-trigger-range-start", "entry 42px");
+test_computed_value("animation-trigger-range-start", "entry-crossing 42px");
+test_computed_value("animation-trigger-range-start", "contain calc(10% + 10px)");
+test_computed_value("animation-trigger-range-start", "entry 1em", "entry 10px");
+test_computed_value("animation-trigger-range-start", "exit calc(1em + 10px)", "exit 20px");
+test_computed_value("animation-trigger-range-start", "cover");
+test_computed_value("animation-trigger-range-start", "contain");
+test_computed_value("animation-trigger-range-start", "entry");
+test_computed_value("animation-trigger-range-start", "exit");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-range-start-invalid.html b/css/css-animations/parsing/animation-trigger-range-start-invalid.html
new file mode 100644
index 00000000000000..6c056d06e96865
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-start-invalid.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942 ">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+test_invalid_value("animation-trigger-range-start", "peek 50%");
+test_invalid_value("animation-trigger-range-start", "50% contain");
+test_invalid_value("animation-trigger-range-start", "50% cover");
+test_invalid_value("animation-trigger-range-start", "50% entry");
+test_invalid_value("animation-trigger-range-start", "50% enter");
+test_invalid_value("animation-trigger-range-start", "50% exit");
+test_invalid_value("animation-trigger-range-start", "contain contain");
+test_invalid_value("animation-trigger-range-start", "none");
+test_invalid_value("animation-trigger-range-start", "cover 50% enter 50%");
+</script>
diff --git a/css/css-animations/parsing/animation-trigger-range-start-valid.html b/css/css-animations/parsing/animation-trigger-range-start-valid.html
new file mode 100644
index 00000000000000..d48151b6db0769
--- /dev/null
+++ b/css/css-animations/parsing/animation-trigger-range-start-valid.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<!-- TODO(crbug.com/390314945): Replace with spec link when the spec lands. -->
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8942">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script>
+// https://drafts.csswg.org/scroll-animations-1/#view-timelines-ranges
+test_valid_value("animation-trigger-range-start", "normal");
+test_valid_value("animation-trigger-range-start", "cover 0%", "cover");
+test_valid_value("animation-trigger-range-start", "cover 100%");
+test_valid_value("animation-trigger-range-start", "cover 120%");
+test_valid_value("animation-trigger-range-start", "cover 42%");
+test_valid_value("animation-trigger-range-start", "0", "0px");
+test_valid_value("animation-trigger-range-start", "120%");
+test_valid_value("animation-trigger-range-start", "120px");
+test_valid_value("animation-trigger-range-start", "cover -42%");
+test_valid_value("animation-trigger-range-start", "contain 42%");
+test_valid_value("animation-trigger-range-start", "exit 42%");
+test_valid_value("animation-trigger-range-start", "exit 1%, cover 2%, contain 0%", "exit 1%, cover 2%, contain");
+test_valid_value("animation-trigger-range-start", "exit 1%, cover 2%, contain 100%");
+test_valid_value("animation-trigger-range-start", "exit-crossing 42%");
+test_valid_value("animation-trigger-range-start", "entry 42px");
+test_valid_value("animation-trigger-range-start", "entry-crossing 42px");
+test_valid_value("animation-trigger-range-start", "contain calc(10px + 10%)", "contain calc(10% + 10px)");
+test_valid_value("animation-trigger-range-start", "entry 1em");
+test_valid_value("animation-trigger-range-start", "exit calc(1em + 10px)");
+test_valid_value("animation-trigger-range-start", "entry 42%");
+test_valid_value("animation-trigger-range-start", "cover");
+test_valid_value("animation-trigger-range-start", "contain");
+test_valid_value("animation-trigger-range-start", "entry");
+test_valid_value("animation-trigger-range-start", "exit");
+test_valid_value("animation-trigger-range-start", "cover calc(sign(100em - 1px) * 1%)");
+</script>
