| keyword | Name of a global shader keyword to enable. |
Adds a command to enable a global keyword with a given name.
If a global keyword with the name you pass in does not exist, Unity creates one with that name when you call this function. To get all the global keywords that already exist, use Shader.globalKeywords. Note: it is more efficient to use EnableKeyword.
另请参阅：DisableShaderKeyword、Shader.EnableKeyword。