Composer дает ошибку «Your requirements could not be resolved to an installable set of packages». Как разрешить?

[32mLoading composer repositories with package information[0m
[32mUpdating dependencies (including require-dev)[0m
[37;41mYour requirements could not be resolved to an installable set of packages.[0m

  Problem 1
    - phpdocumentor/template-abstract 1.2.1 requires ext-xsl * -> the requested PHP extension xsl is missing from your system.
    - phpdocumentor/template-abstract 1.2 requires ext-xsl * -> the requested PHP extension xsl is missing from your system.
    - phpdocumentor/phpdocumentor dev-master requires phpdocumentor/template-abstract ~1.2 -> satisfiable by phpdocumentor/template-abstract[1.2, 1.2.1].
    - Installation request for phpdocumentor/phpdocumentor dev-master -> satisfiable by phpdocumentor/phpdocumentor[dev-master].

{
    "name": "krll_/krll.tk",
    "require": {
        "slim/slim": "dev-master",
        "j4mie/paris": "dev-master",
        "phpdocumentor/phpdocumentor": "dev-master"
    },
    "config": {
        "bin-dir": "bin"
    }
}