userdiff: expand detected chunk headers for css

The regex used for the CSS builtin diff driver in git is only
able to show chunk headers for lines that start with a number,
a letter or an underscore.

However, the regex fails to detect classes (starts with a .), ids
(starts with a #), :root and attribute-value based selectors (for
example [class*="col-"]), as well as @based block-level statements
like @page,@keyframes and @media since all of them, start with a
special character.

Allow the selectors and block level statements to begin with these
special characters.

Signed-off-by: Sohom Datta <sohom.datta@learner.manipal.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/t/t4018/css-attribute-value-selector b/t/t4018/css-attribute-value-selector
new file mode 100644
index 0000000000..918256b20c
--- /dev/null
+++ b/t/t4018/css-attribute-value-selector
@@ -0,0 +1,4 @@
+[class*="RIGHT"] {
+    background : #000;
+    border : 10px ChangeMe #C6C6C6;
+}