Add support for @-o-keyframes and @-ms-keyframes rules

Author: neilime

src/parser/plugins/CssAtKeyframesParserPlugin.php

@@ -73,6 +73,22 @@ public function parse($index, $char, $previousChar, $state)
 			$this->parser->clearBuffer();
 			return $index + 18;
 			}
+		// Start of @keyframes at-rule block (@-o-keyframes)
+		elseif ($char === "@" && $state === "T_DOCUMENT" && strtolower(substr($this->parser->getSource(), $index, 13)) === "@-o-keyframes")
+		{
+			$this->atRuleName = "-o-keyframes";
+			$this->parser->pushState("T_AT_KEYFRAMES::NAME");
+			$this->parser->clearBuffer();
+			return $index + 13;
+		}
+		// Start of @keyframes at-rule block (@-ms-keyframes)
+		elseif ($char === "@" && $state === "T_DOCUMENT" && strtolower(substr($this->parser->getSource(), $index, 14)) === "@-ms-keyframes")
+		{
+			$this->atRuleName = "-ms-keyframes";
+			$this->parser->pushState("T_AT_KEYFRAMES::NAME");
+			$this->parser->clearBuffer();
+			return $index + 14;
+		}
 		// Start of @keyframes rulesets
 		elseif ($char === "{" && $state === "T_AT_KEYFRAMES::NAME")
 			{