提交后保留表单值

我知道有很多像这样的问题，我在网上找到了1000个答案，但没有一个与我的代码一起工作:(所以有人可以帮助我如何保持电子邮件的价值后提交?

        <form name="login-registration" onSubmit="return validateForm()" method="post" action="" >
            <label>Email</label>
            <input type="email" name="emailinput" id="emailinput" value ="" />
            <p id="emptyEmail" class="hidden">Email field is required</p>
            <p id="invalidEmail" class="hidden">Email you insert is invalid!</p>
            <label>Your password</label>
            <input type="password" name="pswinput" id="pswinput" value=""/>
            <p id="pswMinMax" class="hidden">Password should be from 4 to 8 caracters</p>
            <p id="pswLettNum" class="hidden">Password should be letters and numbers. No special caracters are allow</p>
            <label>Repeat password</label>
            <input type="password" name="pswrepeatinput" id="pswrepeatinput" value="" onblur="isValidPswRep()"/>
            <p id="pswR" class="hidden">Your passwords is different</p>
            <input type="checkbox" id="policy" name="policy" value="policy" /> <label>I agree</label>
            <p id="checkN" class="hidden">You must agree to our term</p>
            <input type="submit" name="submit" value="Login" />
        </form>

我试着写一些代码:

<input type="email" name="emailinput" id="emailinput" value = "<?php echo htmlspecialchars($_GET['lastname']); ?>" />

但是php行只是显示在字段输入中。