--- /dev/null
+# function-calc-no-unspaced-operator
+
+Disallow an unspaced operator within `calc` functions.
+
+```css
+a { top: calc(1px + 2px); }
+/** ↑
+ * The space around this operator */
+```
+
+Before the operator, there must be a single whitespace or a newline plus indentation. After the operator, there must be a single whitespace or a newline.
+
+## Options
+
+### `true`
+
+The following patterns are considered violations:
+
+```css
+a { top: calc(1px+2px); }
+```
+
+```css
+a { top: calc(1px+ 2px); }
+```
+
+The following patterns are *not* considered violations:
+
+```css
+a { top: calc(1px + 2px); }
+```
+
+```css
+a { top: calc(calc(1em * 2) / 3); }
+```
+
+```css
+a {
+ top: calc(var(--foo) +
+ var(--bar));
+}
+```
+
+```css
+a {
+ top: calc(var(--foo)
+ + var(--bar));
+}
+```